Arsenal will be sweating on the fitness of Kieran Tierney after he hobbled off in their defeat against Liverpool.
The left-back clashed with James Milner and was forced off before half-time.
Tierney has been integral for the Gunners this term, both in attack and defence, and any long-term absence would be a major blow.
Mikel Arteta revealed that the Scot knew something was up, but will now wait on the diagnosis.
He said: “Kieran felt something in his knee.
“He was in pain so it looks like he will be injured but we don't know how long for.”
Arsenal are still in contention for the Europa League and face Slavia Prague in the last eight.
Arteta will hope that Tierney can play some part but time is very much against him.
Scotland boss Steve Clarke will also be keeping an eye on the situation ahead of this summer's Euros.
Arsenal's hopes of bettering last season's eighth place finish were dealt a blow though in their humbling defeat at the Emirates.
The Reds put in a dominant display and bagged three second-half strikes with the hosts offering little in reply.
Arteta could not hide his frustration in the aftermath but shouldered the blame himself.
He said: “We completely deserved to lose the game, they were better in every department. They deserved to win the game by the margin they did, or more. I can’t accept from our side the way we played today.
"They won every duel, every second ball, every challenge. They were brave when they had the ball, they made the right decisions, we didn’t.
"It is my fault. I have to set the team to play in a different way. Congratulations to Liverpool, who were exceptional today, they can play at that level.
"The margin is incredibly high. The standard has to be much higher for this football club. We could not put three passes together.
"Too many simple things were not done right and when you do that against this opponent you get punished."
