After matchday four of the 2023-24 Champions League group stage, several clubs have booked their place in the round of 16: Bayern Munich, Inter Milan, Manchester City, RB Leipzig, Real Madrid and Real Sociedad.

Manchester United have given themselves a tough task after Wednesday's loss at FC Copenhagen leaves them bottom of their group, Barcelona suffered a shock loss of their own, while Group F could still finish with all four teams -- AC Milan, Borussia Dortmund, Paris Saint-Germain and Newcastle United -- on the same number of points.

We asked our writers Gab Marcotti, Rob Dawson, Alex Kirkland and Julien Laurens to answer some of our burning questions.

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1. United have everything to play for against Bayern and Galatasaray. What will it take to rescue their campaign in the next two games?

Rob Dawson: It starts with being more organised and defending better. They've conceded 11 goals in four games -- only Celtic and Antwerp (two teams who are also bottom of their respective groups) have conceded more in the group stage -- and it's far too many for any team aiming to qualify for the round of 16. As bizarre as it sounds after a 4-3 defeat, Manchester United's performance against FC Copenhagen was one of their better displays of the season. They probably would have won but for Marcus Rashford's first-half red card. There will be cautious optimism ahead of a must-win game in Turkey against Galatasaray on matchday five and after that they'll have to hope Bayern Munich rest players for their trip to Old Trafford.

Julien Laurens: Not making stupid individual mistakes would help! From André Onana's terrible pass against Galatasaray, which led to Casemiro's red card, to Diogo Dalot's horrendous defending in Copenhagen or Aaron Wan-Bissaka's unnecessary back pass. The fact that United have conceded one penalty in each of their first four games in the competition says it all, really. It shows that they are too generous to the opposition when it comes to Champions League matches.

Alex Kirkland: A new coach and a new set of players? No, seriously, Wednesday's defeat was a disaster but a look at the table tells you United are still in contention to progress from the group. They're capable of winning away at Galatasaray and then beating a Bayern side who have already qualified for the round of 16 and might field a weakened team at Old Trafford. But that doesn't mean alarm bells aren't ringing. I was watching Real Madrid at the Bernabeu while United were playing, and couldn't believe the updates coming in from Copenhagen. There's so much wrong at United that it's hard to know where to start. But Ten Hag's position must be under serious scrutiny.

Gab Marcotti: Their biggest problem -- and their biggest strength -- is that Bayern have qualified as group winners. So while Thomas Tuchel will talk a good game about honoring the competition and trying hard in the final two group games, he'd be silly not to send out the second-string, which means we'll probably see more of Frans Krätzig and Aleksandar Pavlovic than Harry Kane and Joshua Kimmich in the last two matches. That'll help United at Old Trafford on Matchday 6. On the flipside, it also helps Copenhagen on Matchday 5. So while you could see United qualifying with eight points, it would also mean it would be out of their hands. Simply put, they need to win in Istanbul. And that's going to be tricky.

2. Which team is your biggest surprise package so far and why?

Laurens: RB Leipzig. Imagine losing four very important players like Josko Gvardiol, Dominik Szoboszlai, Christopher Nkunku and Konrad Laimer in one summer, yet you stay very competitive both in the league and the Champions League. Marco Rose and the club have done an amazing job to replace those departing stars with Xavi Simons, Loïs Openda, Castello Lukeba and Christoph Baumgartner and perform so well. They were minutes away from drawing against Manchester City, and they drew with Bayern in the Bundesliga, too. Simons has been a star, but Leipzig had a plan and they are reaping the rewards now.

Kirkland: Real Sociedad. They've made their return to the Champions League for the first time in a decade look easy. Last time out, in 2013-14, they didn't win a single group game. They began the group by dominating last year's finalists Inter Milan and were unlucky to settle for a draw. They followed that with back-to-back away wins at FC Salzburg and Benfica. And on Wednesday, they scored three goals inside half an hour -- and missed a penalty -- on their way to beating Benfica 3-1 in San Sebastian to guarantee their place in the round of 16. Imanol Alguacil's team are packed with homegrown talent and play fun, attacking football. What's not to like?

Marcotti: Real Sociedad have been the standout team of the group stage, along with Manchester City, the difference being that La Real are doing it on a much slimmer budget. Brais Méndez, Take Kubo, Mikel Oyarzabal give opposing defences fits and, while teams in LaLiga may have figured them out to some degree (which is why they're seventh in the table,) the same can't be said in Europe.

Dawson: Borussia Dortmund keep losing key players like Jude Bellingham, Erling Haaland, Manuel Akanji and Jadon Sancho but, after four games in Group F, they're sat top on seven points. In a group alongside Paris Saint-Germain, AC Milan and Newcastle United, not only have they given themselves a great chance of qualifying for the knockout phase for the fifth time in the last six years, they should also be targeting top spot. They were dealt a blow in the Bundesliga on Saturday with a heavy 4-0 defeat to Bayern Munich, but back-to-back wins over Newcastle have put them in control of their Champions League group. To lose so many top players and continue to challenge in Europe is impressive.

3. Lewandowski has gone six games without a goal for Barca, his worst goal drought in more than a decade. What's gone wrong?

Marcotti: That's a bit of a BS stat, isn't it? Yeah, it's six games, but only four starts. And, in one of those, he came off after half an hour. In fact, he played 90 minutes just twice during that run and in the last couple games was coming off an injury. Yeah, he's old and we can debate whether he was a wise investment from Barca. But he also scored six goals in his first seven appearances this season. Let's wait a while before we write him off, shall we?

Kirkland: It's not just that Robert Lewandowski isn't scoring. He's barely getting into positions to score, either. Against Shakhtar he had two shots, neither on target. In Barca's visit to Real Sociedad on Saturday, he had no shots in just under an hour on the pitch. He had one shot, off target, in his substitute appearance in El Clasico, and none before he was injured against FC Porto. There are mitigating factors, and context to consider. This barren streak comes after six goals in five club games between August and September, and this Barca team struggle to create chances generally, with one shot on target in 90 minutes against Shakhtar. But Lewandowski can't be absolved of all responsibility. He's looking his age (35) and some feel a more mobile forward would suit them better.

Dawson: Lewandowski hasn't turned into a bad striker overnight. He's on a poor run, but he had 33 goals for Barcelona last season and 50 the season before for Bayern Munich. He has eight in seven games for club and country in August and September. The goals will return -- he's too good a player for that not to be the case -- but at 35 years old it's only natural that he will begin to slow down eventually. It doesn't help that Barcelona don't create a ton of chances, but it's also not possible that he's the same player that he was five years ago. Time catches up with even the greatest players.

Laurens: It's a bit of everything. His age and the injuries that he is picking up now are not helping. He has just lost that split-second of sharpness that he used to have and, at this level, it shows. Even last season, despite doing well overall and being LaLiga's Pichichi (top scorer) last season, there were times where you could see he was not as effective. There is also a collective issue. This Barcelona side is not creating enough chances overall, and for him especially. I don't think Haaland would score many more goals than Lewandowski in this side. Xavi has to find a way to bring the creativity back to help his main striker. The return of Pedri is great news on that front.

4. Group F is now wide open after Dortmund and Milan won. Who are your favorites to go through and why?

Dawson: The varying inconsistency of every team in Group F means that they'll all believe they can go through to the last 16, but two big clubs are going out. Newcastle had a spectacular win over Paris Saint-Germain at St James' Park but Eddie Howe is dealing with a mounting injury list and after two defeats to Borussia Dortmund, they are going to find it very difficult. You would fancy PSG to make it three home wins out of three against Newcastle on matchday five, a result which would put them on the brink of qualification ahead of their trip to Dortmund. The German side are best-placed to join them in the knockout rounds but they'll need a good result in Milan next up.

Laurens: PSG are totally unpredictable in the Champions League this season but they are still in a good position. So much so that they could even qualify by beating Newcastle at the Parc des Princes (where they have been dominant in the competition) in three weeks' time, with a trip to Dortmund to follow. The thing is that all the other teams are also inconsistent and unpredictable, especially Newcastle and Dortmund. Milan should have beaten them both but didn't take their chances, but I still fancy them to go through with PSG.

Kirkland: PSG are under pressure after their loss in Milan but they've won both their home games at the Parc des Princes so far and should do the same against Newcastle on matchday five, a result which would put them into the round of 16 if Dortmund beat Milan at San Siro that same night. Luis Enrique's PSG have been up and down so far this season but they still have such incredible talent, and Enrique is an exceptional, if often frustratingly dogmatic coach. Dortmund deserve to join them in the round of 16 after their impressive back-to-back wins against Newcastle.

Marcotti: I can't imagine PSG getting knocked out in the group stage. Even if they don't beat Newcastle at home, they're more than capable of dismantling Dortmund away (never underestimate their ability to self-destruct). I think Milan are well-placed here. They were poor at PSG, but battered Dortmund and Newcastle in terms of chances when they played them (cumulative xG: 3.02 to 1.19). Plus, Newcastle could be eliminated by the time they play them. They obviously need to beat Dortmund at San Siro, but I think they'll get it done (and I have no idea why my colleagues are so bullish on Borussia ... guessing they're big Niclas Füllkrug fans?)