Lee Sharpe feels Ole Gunnar Solskjaer has built a strong squad at Manchester United, but believes striker Anthony Martial represents the "only question mark" for him to solve.
Martial has been criticised this season for his inconsistent performances and has struggled to cement his place as United's leading No.9.
The presence of veteran Edinson Cavani has highlighted the work still to be done if Martial is to fulfil the role long term, and Solskjaer admitted recently it is unlikely the Frenchman will feature again this season due to injury.
And former Man Utd star Sharpe has questioned whether Martial will live up to his full potential at Old Trafford.
Asked if any of United's current crop need replacing, Sharpe, speaking exclusively to Mirror Football in conjunction with William Hill , said: "My only question mark would be the No.9 and Anthony Martial.
"I think he’s been given a lot of chances, he’s had a lot of time at the club and his performances still seem to be a little bit more inconsistent than I would like from my No.9, and he’s probably the only one I’d look to change."
Pressed on whether there was a future for Martial at the club, Sharpe replied: "I’m not sure. I think that’s a decision for Anthony Martial. On his day the guy’s a world beater, he’s unplayable at times, but it doesn’t seem to happen often enough for him.
"His ability is unquestionable. The only thing that is questionable is what’s between his ears and his attitude towards the game.
"Sometimes he seems to be off the pace by quite a margin and doesn’t seem that interested.
"I’m sure that’s not the case, it just doesn't happen for him in certain games and then other games he leads the line and holds the ball up well, brings people into play, scores wonder goals, is cool under pressure, got a great touch and awareness.
"But if [Erling] Haaland or [Harry] Kane came in and Martial had to play second fiddle, would he be happy with that after being such a prominent figure in the team for so long?"
Martial has scored just seven times in 36 appearances in all competitions for United this season - well below his tally of 23 from the last campaign and his lowest so far in a United shirt.
Solskjaer is still hopeful of convincing Cavani to stay on for another season, but beyond that signing Haaland from Borussia Dortmund - or a suitable equivalent - appears to be in the United manager's thinking.
So where does that leave Martial?
"It would be nice to keep him because I still think he’s a quality player and we go back to successful years when Manchester United had three or four centre forwards in one squad and could rotate and change things for different games - that would be the ideal situation," Sharpe added.
"But I think it’s Anthony Martial’s decision really as to whether he would share the No.9 shirt with someone or whether he would want to go elsewhere and be the main man."