Arsenal manager Mikel Arteta is unsure about the status of Shkodran Mustafi after Thursday's draw with Olympiacos saw them knocked out of the Europa League.
The defender had to be withdrawn at the end of the first half of extra time.
Arteta said after the game: "I don't know [how bad it is]. He said to me 'I cannot play anymore'. I'm not sure if it was a cramp or a muscle injury.
"I am sure there will be a few of those [types of injuries] because players were exhausted, they played four times in 11 days and it was physically a very demanding game."