Former Manchester United midfielder Owen Hargreaves feels they're asking too much of Marcus Rashford.
Speaking to Premier League Productions, Hargreaves said he has has doubts over whether Rashford can fill the forward void left by the summer departure of Romelu Lukaku to Inter Milan.
"It's a shame because I love him as a player, I think he's terrific, but they [United] need a No.9," Hargreaves said.
"Sanchez has gone, Lukaku has gone, they needed him to step up. Martial has really taken the No.9 shirt and been great.
"Rashford had a chance [against Southampton] and he didn't take it. Is he going to be a No.9, is he going to play off the left? He didn't capitalise."