Ole Gunnar Solskjaer's 'biggest concern' about his Manchester United team is that Harry Maguire can't be trusted in one-on-one situations, according to Rio Ferdinand.
United's captain isn't known for his speed and this has been known to leave United's defence vulnerable when opponents attack them with pace.
The same issue applies to Maguire's regular partner Victor Lindelof, meaning United are likely to go into the transfer market to buy a new defender in the summer.
And it's been noted by former United centre-half Ferdinand, who suggested it's something Solskjaer must address to keep his team progressing.
'I think that's Ole's biggest concern - can he leave Maguire one v one on the halfway line? Or Lindelof?' Ferdinand told his YouTube channel.
'It's proven that you can't as that's not their main attributes.
'Harry Maguire is good at a lot of other things but that area, that's one of his weak points.'
United are drawing up a shortlist of centre-back targets for the summer window as they look for someone to partner Maguire instead of Lindelof or Eric Bailly.
Speed in tracking back to support Maguire is likely to be the key attribute United are looking for.
By contrast, right-back Aaron Wan-Bissaka excels in one-on-one situations, as shown when he marked Raheem Sterling out of the recent Manchester derby, but needs work on playing out from the back.
Ferdinand said: 'I think Wan-Bissaka can be coached into that, I think he's going to have to do a lot of work on the training ground on the ball and with the ball.
'His strongest point, we saw against City, his ideal scenario is to be left one v one against the wide man. There's nobody better around than him.'
United return to action away to AC Milan in the second leg of their last-16 Europa League tie on Thursday night with the scores level at 1-1 after the first leg.
