The Red Devils striker faces a lengthy spell on the sidelines after suffering a double stress fracture of his back.
Former Tottenham midfielder Jamie O’Hara suffered a similar injury during his playing career, and criticised United’s medical team for passing Rashford as fit for the game.
“It’s a bad injury to get and I can’t believe that the medical team at Man United have allowed him to carry on playing,” O’Hara said. “They must have known he had a stress fracture.”
“They must have been worried about his back, he’s gone for an X-ray and they’ve seen. Footballers will always say, ‘I’m all right’. But there needs to be a time when there is protection for a player who is at Manchester United .
“Now United have lost him at the most crucial period of the season and potentially England have lost him.”
Rashford was absent for United’s defeat to Liverpool on Sunday, and could now miss up to three months of the season.
He also faces a race to be fit in time to be included in England’s squad for Euro 2020.
United boss Ole Gunnar Solskjaer claimed Rashford could yet return within the next six weeks, but O’Hara was sceptical.
“For Solskjaer to say he’s going to be back in six weeks from that injury is ridiculous. He ain’t going to be back in six weeks to my mind. A double stress fracture to the spine is a three months injury minimum.
“I wouldn’t expect to see him back until the last stages of the season and that’s if he’s lucky – if he heals well. He is young. But he may have to have surgery.
“I ended up having two screws and a rod put in my spine, they put bone marrow out of my hip and packed it into my spine because the fracture wouldn’t heal because it was in such a difficult position.
“It’s a major injury that and I’m gobsmacked they’ve allowed him to continue playing at that age.”