David Moyes has described Lynden Gooch's ankle injury as a terrible blow - with the "infectious" midfielder facing up to three months on the sidelines.
The 20-year-old has broken onto the first team scene this season but is facing a lengthy spell out after being carried off with the injury in the Under-23 draw with Tottenham Hotspur earlier this week.
Gooch was in London on Friday to see a specialist, who will decide if surgery is needed on the ankle ligament damage but either way he is facing up to 12 weeks out.
"Unfortunately Lynden was taken off for the reserves and it looks like damage to one of his ligaments," Moyes told the Echo.
"He is seeing the surgeon today to see if he needs an operation but he will be out for somewhere between eight and 12 weeks, depending on what the surgeon says.
"It is a terrible blow for Lynden, we like him, he is infectious. He is a good character.
"I was speaking to him last week and told him that I thought his levels had dipped but that would be normal for a young player especially if you think of the games we have asked him to play in and the situation of the team.
"I have seen his training coming back, though, in recent weeks and this is a real blow for him.
"Him and Paddy McNair getting Premier League games is a big part for their development. To lose him has been a big blow."
The blow has been softened with the return to fitness of Seb Larsson, who was on the bench against Liverpool and Jan Kirchhoff, who could be on the bench against Leicester City.
The German midfielder had a sickness bug at the start of the week but has taken part in training this week.
Moyes added: "Seb and Jan are both back in, Kirchh is still a worry, though. He is back training but he was sick and missed a couple of days which hasn't helped.
"I have a decision to make, he didn't get all the week's training in that I would have hoped so I need to assess him."
Jack Rodwell will also miss out again, the midfielder is not expected to return from his hamstring injury for another couple of weeks.
Moyes hopes to have him back involved and ready for selection in time for the festive period.
"Jack is not training yet. I wouldn't say he has had a set-back, it was a bad hamstring injury which he did in training," added Moyes.
"It looked like a real six week job, Jack won't be back too quick.
"We could do with getting him back somewhere in the middle of December if we can, to get him back for the games over the Christmas period."