London Irish boss Brian Smith revealed serious concern for England prop Alex Corbisiero after his side's 18-12 win over Gloucester.
Corbisiero pulled out in the captain's run before the trip to Kingsholm, with Smith describing his knee problem as a "degenerative condition" that could rule him out of Irish's upcoming fixtures and the Six Nations.
"It is very frustrating for us, it is very frustrating for 'Corbs'. It is a tough time for him, and it is a difficult one to balance," said Smith.
"His knee is a mess. He has played one-and-a-half games for us this season, and it is very disappointing.
"Sitting here right now, I couldn't tell you if he is going to play next week or not. He has got degenerative knee issues. He trained twice this week. We are bringing him back, and then at the captain's run he pulled out prior to it, and we had to make a change.
"There is not much of a decision to make when a bloke's knee has blown up and he feels he can't play. You can't put a gun to his head and tell him to get on the paddock.
"He is an honest person, he is a good bloke. He desperately wants to play for us, but it is a very frustrating situation."
Irish's stunning victory was their first away win of the season, with lock George Skivington grabbing a brace to move the Exiles five points clear of bottom club Sale.
"We picked a big pack so we could go toe-to-toe with them. The game could have gone either way, that is fair to say, but we came out on top," added Smith.
"The team showed a lot of character and toughed it out. I thought the whole pack was immense today. It was won up front."
Gloucester boss Nigel Davies was left frustrated by his team's outing as they lost at home for the first time since the opening game of the season against Northampton.
"We are hugely disappointed," said Davies.
"The important thing is that when you lose games, it's how you deal with it, manage it and come back. Today showed we are not good enough to slip off the hard work, intensity and accuracy.
"When we do that, like we we did today, then we were second best. We had little control over the game. Our set-piece didn't function, which put a bit of pressure on us, and there were far too many errors in our game."