As we have seen over the past 18 months, due to the COVID-19 pandemic and its impact on the global financial market, clubs will have to get creative if they are looking to move players on, or bring in new arrivals.

The transfer rumour mill is still turning but it is unlikely that any of Europe's top clubs will spend €100 million on one player this summer, as they have done in the past. Transfer values have shrunk, and clubs are cutting costs, but swap deals could be the salvation.

There's a few high-profile precedents from history (although it didn't work out that well) as Zlatan Ibrahimovic and Samuel Eto'o traded between Barcelona and Inter Milan in 2009, along with a host of others over the years.

With the caveat that they are all hypothetical, here's a list of swap deals that big clubs could try to pull off in the transfer market to get what they want. *All market values by Transfermarkt.

Man United's De Gea and Van de Beek FOR Atletico's Oblak and Trippier

Deal total worth: €90m for Jan Oblak (€70m) and Kieran Trippier (€20m)
Swap players' value: David de Gea (€20m), Donny van de Beek (€30m) plus €40m cash

Spanish champions Atletico Madrid are in a tough financial position and need to raise funds, while also replacing any player that goes. Their star goalkeeper Oblak would be tough to replace, but it's difficult to think of a better option than De Gea, who started his career at Atletico before moving to Man United in 2011. De Gea is 30 and has a contract which expires in 2023, so his value isn't going to increase but he's only two years older than Oblak and can reignite his career back in La Liga. Yes, United have Dean Henderson as well, and he'd probably have to be moved on or sent out on loan, but Oblak is world-class and arguably the best goalkeeper around. Atletico would have to lower their €120m asking price considerably, but knowing they'd get De Gea in return might do it.

United have shown interest in Trippier already to strengthen their full-back positions, so it makes sense to add him to the deal, while realising that a 30-year-old defender isn't going to fetch his €40m release clause. As a sweetener, United can add Van de Beek, who has struggled since his €45m arrival from Ajax last summer, and he would be able to slot in and replace Saul Niguez (who looks likely to depart) in the Atletico midfield.

Real Madrid's Varane and Rodrygo FOR PSG's Mbappe

Deal total worth: €160m for Kylian Mbappe
Swap players' value: Raphael Varane (€70m and Rodrygo (€40m), plus at least €50m cash.

Real Madrid's interest in signing Mbappe is no secret, nor is the player's desire to one day join the Spanish club. But a €160m deal just can't be done in these times, even with Mbappe's contract running down in 2022. He surely won't want to leave his hometown side short by moving on a free transfer next summer, so one would imagine he'll sign new terms in the coming months to keep his value, perhaps with a release clause written in should Madrid make an acceptable offer.

But to head all that off, Madrid are in a strong position to offer PSG a pretty good deal right now. They have an unhappy Varane wanting to return to France, with his contract expiring in 2022 as well, and a young player who could slot in to Mbappe's position. Rodrygo hasn't impressed as much as fellow Brazilian Vinicius Jr. at the Bernabeu since his arrival in 2019 but he's only 20 and PSG could certainly help him push on to the next stage of his career.

Madrid get their No. 1 target; PSG get a world-class defender and a forward with huge potential. Madrid would have to raise another €50m to even tempt PSG into discussions but they have a host of players like Isco, Mariano Diaz and Alvaro Odriozola who could get them there if they are moved on.

Arsenal's Lacazette FOR Lyon's Aouar

Deal total worth: €42m for Houssem Aouar
Swap players' value: Alexandre Lacazette (€28m), plus at least €14m cash.

Arsenal offered €35m for Lyon midfielder Aouar last September, sources told ESPN, but didn't end up managing to make a deal with the French club. Their desire to sign a creative midfielder is still high, but the fact they missed out on Europe for next season will be an issue. If they can persuade Aouar that his future is in London, then Lacazette would make an excellent makeweight as the Gunners can offload him for around €28m, even though his contract expires in 2022.

Lacazette is 30 and could be tempted to return to his former club, he would have to accept a drop in wages but at least he'd get to play European football.

Juve's Ronaldo and Ramsey FOR Man United's Pogba

Deal total worth: €60m for Paul Pogba
Swap players' value: Cristiano Ronaldo (€45m) and Aaron Ramsey (€15m).

Juventus need to reduce their massive wage bill and one place to start would be with star man Ronaldo. The 36-year-old has a contract until June 2022, which earns him around €31m-a-year, but he is reportedly keen to move on as the club struggled in both the Serie A title race and the Champions League last season. Replacing a player of Ronaldo's quality is never easy, while he is on his own planet from a marketing perspective, but it may be time to move him on and getting Pogba in return isn't a bad deal. United wanted around €100m when Juve showed interest in Pogba before, but his value has dropped to €60m given his contract expires next summer.

Having signed on a free transfer from Arsenal in 2019, Ramsey is on €7m-a-season at Juve and the club are reportedly willing to let him go as his career in Turin has been hampered by injury. Adding this pair would give the United squad a boost at no outlay beyond wages, for which both players would need to accept a drop, and star power with Ronaldo's headline return to Old Trafford. Just imagine what the likes of Marcus Rashford and Mason Greenwood could learn from him.

Barcelona's Roberto and Dembele FOR Man City's Silva and Laporte

Deal total worth: €105m for Bernardo Silva (€60m) and Aymeric Laporte (€45m)
Swap players' value: Sergi Roberto (€18m), Ousmane Dembele (€50m), plus €37m in cash

Barcelona's financial situation is well known, €1.2 billion in debt and a wage bill needing to be dropped significantly. Two players who seem expendable to them could be of great interest to Pep Guardiola at Man City. Sergi Roberto is still only 29 and can play a number of different positions, which would help City's strength in depth, and while the club's forward options are strong, a move for winger Dembele would allow Phil Foden and Kevin De Bruyne to operate more centrally. He's had his injury issues but Guardiola may view a €37m profit on top of landing two quality players as a plus. City would have to get another centre-back to replace Laporte, though they may opt to bring in Real Madrid's Sergio Ramos on a free transfer just for a year or two instead.

From the Barcelona angle, it's hard to think of a better player to fit into their system than Silva. His style is perfect and he is reportedly keen to leave City, which comes as something of a shock given how well he has played in England. Sources told ESPN that Barca would also love to pair Laporte with new arrival Eric Garcia (signed on a free from City this summer) as coach Ronald Koeman would also like to add another more experienced centre-back to his squad. But if this deal is to come off, they'll need to raise an extra €37m or so to keep City happy -- which means moving on Clement Lenglet, Miralem Pjanic, Samuel Umtiti or Philippe Coutinho as well.

They'll have enough squad options to replace Roberto and Dembele, but after Sergio Aguero also headed to Camp Nou this summer, they may start to look like Manchester City circa-2020.