We asked the Soccer Saturday pundits what the Premier League's top six need before the transfer window closes on January 31.

Manchester United and Arsenal have just completed the exchange of Alexis Sanchez and Henrikh Mkhitaryan, while Liverpool spent £75m on Virgil van Dijk before selling Philippe Coutinho to Barcelona for £146m.

But what do the league's top sides still require to boost their respective aspirations? Paul Merson, Matt Le Tissier, Charlie Nicholas and Phil Thompson provide their verdicts...

Manchester City

Charlie says: I actually think Pep Guardiola would be interested in a No 9. He might leave it until the summer but if the right option came up I think he would take it because I can't see Sergio Aguero being at the club next season.

Guardiola moved Lionel Messi to the No 9 role so that he didn't have to come deep and I think Aguero drops back into deeper positions too often. It agitates him when his striker stops stretching a defence by coming short and disrupting the fluency of the likes of David Silva and Kevin De Bruyne.

Charlie suggests Sergio Aguero's days at Man City are numbered

Guardiola will have wanted Alexis Sanchez to come in and create space by pushing the defence back. Aguero failed to do that enough against Liverpool and we know what happens to players who fail to adapt under Pep.

I know they're talking about Vincent Kompany coming back soon but I still think they need another centre-back, while they are lacking a natural left-back in Benjamin Mendy's continued absence.

I could also see Claudio Bravo pushing for a move away in January and they would need another back-up goalkeeper if that happens, so it is not all plain sailing for the runaway leaders.

Manchester United

Merse says: I just think Sanchez gets you into the top four - job done. I watched United against Burnley and they were efficient, but Sanchez gives you that x-factor in tight games and his energy drives you forward. After that I'm not sure if they need anything.

Alexis Sanchez guarantees a top-four finish for Man Utd, according to Merse

The big question is when Marcus Rashford and Jesse Lingard are going to play again as Sanchez, Anthony Martial and Romelu Lukaku are going to start now, so they are fighting to come on for Martial.

If I was Arsenal manager I would have tested the water with getting Michael Carrick as United wanted Sanchez more than Arsenal needed Mkhitaryan. Arsenal need somebody who can sit in front of the back four and spray passes around because the current players are not disciplined enough.

Chelsea

Merse says: I would say their main priority would be a centre-forward. Michy Batshuayi played well against Brighton but I don't think he is the answer if Alvaro Morata gets a bad injury.

If Edin Dzeko arrived I think he would be coming to be the main man rather than just play back-up for Morata, which would also open the door for Batshuayi to leave.

Edin Dzeko is odds-on to join Chelsea this month

Can they get anyone else in to strengthen the squad? I'm not so sure. With the big teams I always think you need to be looking at signings who can come in and deliver over the course of 10 games and that sort of quality is difficult to find in January.

They will need to strengthen a lot in the summer, though, if they are going to have any chance of closing the gap on Manchester City.

Liverpool

Thommo says: The Emre Can situation is a blot on the copybook as I think he has already agreed a move to Juventus. Players are running the contracts down to get the big payday, like Sanchez did, and if it drags on beyond January then he is definitely not going to sign a new deal at Liverpool.

Naby Keita is set to join Liverpool in the summer

I can't really see any other business being done as the target has to be signing quality and that is tough to find in the final week of the winter window, unless we could convince Leipzig to let us have Naby Keita early.

I don't see that happening, though, but with Adam Lallana getting back to fitness and Virgil van Dijk already signed, Liverpool should still have enough for a top-four finish.

Tottenham

Le Tiss says: I would probably say another option to play in one of the three spots behind Harry Kane. As soon as one of Dele Alli, Heung-min Son or Christian Eriksen are injured you are looking at Moussa Sissoko coming in to replace them, so maybe somebody who can offer something a bit different with pace and quality.

Spurs missed Christian Eriksen's influence against Southampton

I guess a better back-up goalkeeper would help but it is a similar situation to finding a better back up to Harry Kane, as not many top players want to sit on the bench.

I think Eric Dier has been poor this season but they've got Victor Wanyama to come in, so in general I would say they are pretty solid.

Arsenal

Charlie says: The prospect of Pierre-Emerick Aubameyang arriving is really positive as he has that genuine pace to give us a big lift.

It still won't help the area where Arsenal are weak which is defensively. I don't know who can come in now because at this time of the year I don't know if there is much out there we would really want.

Pierre-Emerick Aubameyang has been linked with Arsenal

I would like a centre-back with real pace and toughness because that is what Arsenal are really lacking and I would hope the club, with the new head scout (Sven Mislintat) we appointed from Germany, would be looking at bringing in.

I would take Jonny Evans but I don't think he is better than we have currently got ability-wise in Rob Holding and Calum Chambers, although they don't seem to be progressing.