Phil Jones' participation in the World Cup looks to be in grave danger after he was taken to hospital with a shoulder injury sustained in Manchester United's 3-1 win over Hull.
Jones clattered into Hull defender Maynor Figueroa while jumping for a corner in the 16th minute of the match at Old Trafford.
The 22-year-old England defender walked off the field and down the tunnel moments later, wincing with pain.
Jones was taken straight to hospital, where his left shoulder will be assessed.
England's World Cup squad is named on Monday, but United interim manager Ryan Giggs admits the defender could miss out.
"He has gone to hospital. We'll just have to assess it, but it didn't look great," Giggs said.
"Straight away he knew he had done something.
"He wanted to come straight off. Usually, as a player, you know it's something bad when you do that.
"Hopefully it's not too bad."
Jones has been capped nine times by his country, and was more than likely to make Roy Hodgson's 23-man squad.
The England boss already has defensive injury concerns ahead of the announcement.
Tottenham defender Kyle Walker could be excluded due to a pelvic injury which has sidelined him for the last two months.
Walker's Tottenham team-mate Andros Townsend has already been ruled out through injury, and so has Arsenal winger Theo Walcott.
Manchester United striker Wayne Rooney has missed the club's last two games with a groin problem.