Gary Neville has criticised Anthony Martial's inconsistent performances despite his winning goal in Saturday's 1-0 win over Tottenham.
The Frenchman has started just three Premier League games so far this season, often finding himself used as a substitute.
And Neville has stressed that Martial must perform at his best more regularly and not just in big games if he is to maximise his potential.
“It’s been a stop-start Manchester United career for Martial,” he told The Gary Neville Podcast.
“For someone of his talent, he should be tearing this league apart with his ability. He’s lost his place in the France squad. There’s obviously something wrong with him.
“Mourinho and the French manager has turned off of him a little bit. You always get the feeling he’s playing at 85 per cent. If he showed that extra 15 per cent, then he could do anything. He’s got everything you’d want: composure in front of goal, great skill, pace, strength, but what is that little bit missing?
“The best players in the world don’t have ‘buts’ – the likes of Luiz Suarez, Cristiano Ronaldo, Lionel Messi – there are no buts. Martial is well off that category but that’s where he’s got to be looking. He’s worth £50m and with that talent, he’s got to step up.
“He scores in big games, he takes big moments on and obviously has the temperament to play in big games. But come on, let’s see it every single week.
“He could be a player that could score 20 goals in 20 games if he really wanted to and strived to be the best.”