Tuesday, Aug. 31 is transfer deadline day (11 p.m. BST / 6 p.m. ET) when the summer window closes for 2021, meaning all the big clubs are racing to fill gaps in the squad, find new teams for fringe players (either permanently or on loan) or figure out the financials to make a late big move.

Europe's top teams have done some mega business already, with Manchester United landing Jadon Sancho, Raphael Varane and now Cristiano Ronaldo, while there has been at least one big signing for most other clubs like Manchester City (Jack Grealish), Chelsea (Romelu Lukaku), Arsenal (Ben White), Barcelona (Sergio Aguero), Real Madrid (David Alaba), Bayern Munich (Dayot Upamecano), and of course Paris Saint-Germain have made lots of world-class additions (Lionel Messi, Gianluigi Donnarumma, Sergio Ramos, Achraf Hakimi.)

Tottenham striker Harry Kane is staying for now, meaning that's one saga put to bed, but will PSG forward Kylian Mbappe get a €180m move to Real Madrid before the window closes? And what other business do the top clubs need to do before they are stuck with their squad until January?

ESPN's correspondents and writers take you through what might happen over the remaining hours.

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Premier League teams

ARSENAL

Notable Ins: DF Ben White, MF Martin Odegaard, GK Aaron Ramsdale, MF Albert Sambi Lokonga, DF Nuno Tavares
Notable Outs: DF David Luiz, MF Joe Willock, MF Matteo Guendouzi, MF Lucas Torreira

Arsenal have plenty of players available for the right offer -- including Hector Bellerin, Ainsley Maitland-Niles and Sead Kolasinac -- but have left themselves too much to do in terms of moving players out and bringing in adequate replacements. Their awful start to the season and desperate need for reinforcements point to a frantic final few days and the risk of mistakes being made.

The big dilemma for Mikel Arteta and the club's financial team is what to do with strikers Alexandre Lacazette and Pierre-Emerick Aubameyang. Lacazette is out of contract in June 2022 and has so far attracted no interest, but to unlock further funds for late reinforcements, sources said that the Gunners could be prepared to offload their most experienced goal-scorer Aubameyang, despite manager Mikel Arteta saying he will stay.

If that does happen, another striker would be needed as Eddie Nketiah could depart on loan -- Crystal Palace are interested, though a deal appears unlikely -- along with winger Reiss Nelson, while a right-back will be needed if Bellerin gets his wish to leave. Norwich's Max Aarons has been linked there. -- Mark Ogden

CHELSEA

Notable Ins: FW Romelu Lukaku
Notable Outs: FW Tammy Abraham, DF Fikayo Tomori, FW Olivier Giroud, DF Kurt Zouma

The European champions have already addressed their most obvious weakness by signing striker Romelu Lukaku for €115m from Inter Milan, but they remain keen on strengthening their centre-back options. Sevilla's Jules Kounde remains their preferred option, though the Spanish side are asking for closer to €65m to complete a deal, having previously indicated they'd be willing to accept €50m plus add-ons. This might make a deal less likely, but Chelsea still have time after Kurt Zouma moved to West Ham for around £25m.

Midfielder Tiemoue Bakayoko is leaving again on loan to AC Milan, with a loan move for Atletico Madrid midfielder Saul Niguez a possibility as he seeks an exit from LaLiga's reigning champions. Chelsea still have the likes of Danny Drinkwater, Ross Barkley and Ruben Loftus-Cheek on the books and may consider moving them on if they can, while winger Callum Hudson-Odoi is reportedly in talks with Dortmund over a loan move. -- James Olley

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LIVERPOOL

Notable Ins: DF Ibrahima Konate
Notable Outs: MF Georginio Wijnaldum MF, Harry Wilson, FW Xherdan Shaqiri

Manager Jurgen Klopp has no major holes to fill in his squad, and the priority in recent weeks has been finalising new contracts for Virgil van Dijk, Trent Alexander-Arnold, Mohamed Salah, Jordan Henderson, Sadio Mane and Roberto Firmino.

The summer exit of Georginio Wijnaldum to PSG has left Liverpool without one of their most consistent performers of recent seasons and a decision could be made to find a replacement -- with Brighton's Yves Bissouma linked -- but right now, Klopp is happy to rely on Fabinho, Henderson, Thiago Alcantara and Curtis Jones to fill the gap.

The likes of Divock Origi, Takumi Minamino, Alex Oxlade-Chamberlain and Naby Keita are all potentially available for the right offer. Aston Villa also want to sign Curtis Jones on a permanent deal (valued at around £15m), which gives Klopp another decision to make. But in terms of big arrivals, Liverpool are unlikely to make significant moves. Liverpool believe their squad is strong enough to compete on all fronts, meaning a quiet final day of the window is the most likely outcome at Anfield. -- Ogden

MANCHESTER CITY

Notable Ins: MF Jack Grealish
Notable Outs: FW Sergio Aguero, DF Eric Garcia

Pep Guardiola says he's happy with his squad, but after the departure of Sergio Aguero to Barcelona, there's clearly room for a striker. City never hid the fact they want to sign Harry Kane, but that's not going to happen now the England captain has committed his immediate future to Tottenham.

Sources have told ESPN that Spurs flatly refused to negotiate over Kane and it's worth noting that, in the past, City have walked away from the negotiating table and waited a year to strengthen like they did with Ruben Dias in 2020.

With no Kane arrival, the odds are on City not signing a striker before the deadline. Options will, of course, be looked at but time is running out and City don't usually panic. They won the league and reached the Champions League final with a broadly similar squad -- Aguero has left; Grealish has come in -- and they will back themselves to do the same again. -- Rob Dawson

MANCHESTER UNITED

Notable Ins: FW Jadon Sancho, DF Raphael Varane, FW Cristiano Ronaldo
Notable Outs: DF Axel Tuanzebe, MF Andreas Pereira, FW Facundo Pellistri

Manchester United spent their summer budget on Jadon Sancho and Raphael Varane, and executive vice-chairman Ed Woodward had to find funds from elsewhere to make sure they were ready to wrap up a deal for Cristiano Ronaldo when the chance presented itself. Because of that, it is highly unlikely they will make any more signings on deadline day, but a club like United would always explore an opportunity. Just look at Ronaldo.

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Dan James could possibly move to Leeds United -- either permanently or on loan, with Brighton also keen -- and there is always a chance someone could come in for a bid for either Diogo Dalot or Jesse Lingard, although it looks likely both will stay at Old Trafford. Amad Diallo was set to move on loan to Feyenoord, but a thigh injury suffered in training means he will now stay to complete his recovery. -- Dawson

TOTTENHAM

Notable Ins: MF Bryan Gil, DF Cristian Romero, GK Pierluigi Gollini, MF Pape Matar Sarr
Notable Outs: DF Toby Alderweireld, FW Erik Lamela, MF Moussa Sissoko

The longest-running transfer saga of the summer looks like it's over as Kane revealed he was staying at Tottenham amid interest from Manchester City. Spurs wanted £150m for the England national team captain, but City did not even make an offer as there was clearly no room for negotiation.

Spurs chairman Daniel Levy's name is synonymous with last-minute activity and the club retain an interest in Wolves winger Adama Traore. Meanwhile, they are still looking at options in the centre-back and right-back positions as well, with links to Barcelona's Emerson -- the Spanish side rejected one offer from Spurs this weekend -- as well as Fiorentina's Nikola Milenkovic and Bologna's Takehiro Tomiyasu.

In midfield, Barcelona's Ilaix Moriba -- though RB Leipzig are favourites to sign the 18-year-old -- Lyon's Houssem Aouar and Cagliari's Nahitan Nandez could be options as the club are open to letting Tanguy Ndombele and Serge Aurier depart.

Spurs have already completed a deal for Pape Matar Sarr, but have loaned the midfielder back to Metz for the season. -- Olley

European teams

ATLETICO MADRID

Notable Ins: MF Rodrigo de Paul, MF Benjamin Lecomte, FW Matheus Cunha
Notable Outs: FW Vitolo Machin, GK Ivo Grbic

This was never going to be a busy transfer window for Atletico, given their precarious finances and a strong squad that just won LaLiga ahead of Real Madrid and Barcelona. Rodrigo de Paul already looks like a shrewd addition who adds much-needed creativity.

The one piece of business needed was to land a forward to add depth up front and Hertha Berlin's Matheus Cunha is that €30m arrival. That said, it will be interesting to see how Cunha adapts to Atletico: Simeone's record in moulding talented creative players to suit his rigorous system and demanding style is mixed, to say the least.

One big departure could be midfielder Saul Niguez, who has seen interest from Man United and Chelsea in the Premier League, but so far there has been no offer. Nehuen Perez has moved to Udinese on loan, Santiago Arias will join Granada and Lille's Zeki Celik has been linked as his replacement. -- Alex Kirkland

BARCELONA

Notable Ins: FW Memphis Depay, FW Sergio Aguero, DF Eric Garcia, DF Emerson Royal
Notable Outs: FW Lionel Messi, DF Junior Firpo, FW Konrad de la Fuente

Barca would still love to bring in a new midfielder, another attacker, a backup for left-back Jordi Alba and even another centre-back eventually. The financial reality, though, is that more signings are unlikely, if not impossible, this summer.

If some money does magically appear, sources have told ESPN that coach Ronald Koeman would prioritise the arrival of another forward. Despite already adding Memphis Depay and Sergio Aguero (who's out injured for two months) to the squad, Koeman still feels work needs to be done to replace the output of Lionel Messi, who was the top scorer in LaLiga last season with 30 goals.

Yet the biggest thing Barca need to accomplish on the final day is reducing the wage bill, as Messi's exit hasn't fixed all their financial problems. One big earner who they expect to leave is Miralem Pjanic, who has offers to return to Italy, but Samuel Umtiti has opted against accepting any of the offers he's had this summer, much to Barca's chagrin. He will stay as the club's sixth choice centre-back.

Youngster Alex Collado will also be allowed to leave, while president Joan Laporta has admitted they will pretty much entertain offers for most of their players. However, at this stage of the window, a lack of solid interest in the likes of Antoine Griezmann, Philippe Coutinho and Ousmane Dembele means there are unlikely to be any big transfer fees coming in to improve the club's financial health. Ilaix Moriba is expected to join RB Leipzig for around €20m, though, and Tottenham may return with an improved bid for right-back Emerson Royal after their first offer was rejected. -- Sam Marsden

BAYERN MUNICH

Notable Ins: DF Dayot Upamecano, DF Omar Richards, MF Marcel Sabitzer
Notable Outs: DF David Alaba, DF Jerome Boateng, MF Javi Martinez

The biggest need for Bayern is to strengthen at centre-back and in midfield. They need Lucas Hernandez to be fit again so he can partner new arrival Upamecano, but they're running out of time to add another player to replace the departed David Alaba before the window closes -- Borussia Monchengladbach's Matthias Ginter is a possible option.

At least they've addressed a similar need in midfield with the arrival of Marcel Sabitzer from RB Leipzig. They expect Corentin Tolisso to leave before the deadline and Sabitzer, the Austrian international who worked and developed so well under Bayern's new manager Julian Nagelsmann at Leipzig, will offer a strong third option alongside Joshua Kimmich and Leon Goretzka. A rumoured move for Gladbach's Jonas Hofmann has reportedly collapsed and won't happen now.

Though it won't be decided on deadline day, the biggest decision that Bayern face is what to do with Robert Lewandowski's contract. It expires in two years, but the recent stories about the Poland international wanting "a new challenge" could push Bayern to sell or extend the 33-year-old's current deal. PSG have tested the water in recent days for the striker but Bayern are not selling. However, talks with Lewandowski and his agent, Pini Zahavi, could start during the season to keep him at the club for a bit longer. -- Julien Laurens

BORUSSIA DORTMUND

Notable Ins: GK Gregor Kobel, FW Donyell Malen
Notable Outs: FW Jadon Sancho, MF Thomas Delaney

Seeing Dortmund play under Marco Rose so far this season, it is quite clear to see what they need the most: a defence! Axel Witsel, the Belgium international midfielder who is deputising at the back, is not doing a great job there so far and the club is working hard to strengthen the squad in these positions. Marin Pongracic, the Wolfsburg centre-back, will likely join in a loan deal with an option to buy, while right-back Diogo Dalot could also sign on loan from Manchester United.

Dortmund also need a wide player to replace Sancho despite having plenty of wingers in the squad. Dortmund really like Chelsea's Callum Hudson-Odoi and a loan move could well happen before Tuesday night, while Thomas Delaney's transfer to Sevilla means the club also need a central midfielder, with Eduardo Camavinga one of the targets, but time is playing against Dortmund to finalise a deal for the French prodigy.

Barring something crazy from PSG (and don't rule it out in this transfer window of all transfer windows) Erling Haaland will stay for one final season before leaving for €75m next summer. Otherwise, the club will wait until January to see if they need to readjust their squad and plan for more moves. -- Laurens

PARIS SAINT-GERMAIN

Notable Ins: FW Lionel Messi, DF Achraf Hakimi, DF Sergio Ramos, GK Gianluigi Donnarumma, MF Georginio Wijnaldum
Notable Outs: DF Mitchell Bakker

It has been an incredible window for PSG, but would that change if Kylian Mbappe leaves? PSG held firm when €180m was offered, despite the fact the 22-year-old star can leave for free in 12 months' time at the end of his contract. Real Madrid are still negotiating and pushing hard to complete a deal before the window ends and PSG would likely target Bayern's Lewandowski, Dortmund's Erling Haaland, or Everton's Richarlison should Mbappe move, sources have told ESPN.

Highly rated Rennes midfielder Camavinga -- who has just one year left on his contract and would be an absolute bargain at €30m -- is also really keen to join the club. Manager Mauricio Pochettino and sporting director Leonardo like him a lot, though he would only arrive if PSG make space in the squad first.

Indeed, the biggest need for PSG right now is to thin their squad. They had planned before the summer to raise roughly €180m from player exits and are still far from that number, unable as yet to find clubs for fringe players like Pablo Sarabia, Thilo Kehrer and Layvin Kurzawa. -- Laurens

REAL MADRID

Notable Ins: DF David Alaba
Notable Outs: DF Sergio Ramos, DF Raphael Varane, MF Martin Odegaard

Real Madrid haven't paid a transfer fee to add to their first-team squad since the summer of 2019. Part of that has been about adjusting to the new financial reality brought about by the COVID-19 pandemic; part of it has been a recognition that they can no longer go toe-to-toe as equals with the likes of Paris Saint-Germain and Manchester City; and part of it has been about saving up for president Florentino Perez's first-choice, dream signing: Mbappe.

That financial prudence -- including the money brought in from the exits of Varane and Odegaard this summer -- has put Madrid in a position to make a €180m offer for Mbappe, though why they aren't waiting until next summer when he's available for nothing is another question, especially as negotiations appear to be at a standstill following discussions before the weekend.

Casemiro, Karim Benzema, Thibaut Courtois, Federico Valverde, Luka Modric, Dani Carvajal, Lucas Vazquez and Nacho Fernandez have all been signed up to new contracts but there will only be one new addition this summer if at all. In short, it's Mbappe or nothing. -- Kirkland