Arsene Wenger believes Arsenal captain Mikel Arteta will "be out for a while" with the calf injury he sustained during the 2-0 victory against Borussia Dortmund on Wednesday.
Yaya Sanogo and Alexis Sanchez were both on target as the Gunners guaranteed their place in the Champions League last-16 with a match to spare.
Arteta, however, limped off during the second half at the Emirates Stadium and Wenger is not optimistic about his chances of being fit for Saturday's match at West Brom.
"That doesn’t look good, it’s the calf," he told Sky Sports. "It’s very difficult to take on the chin because we are going into many games and you need everybody available, but I think Arteta will be out for a while."
Wenger also praised Sanogo, who opened the scoring after just two minutes but picked up a hamstring injury in the second half, and says he is still unsure if Jack Wilshere will need surgery after injuring his ankle against Manchester United on Saturday.
"I liked what he did tonight because we decided to go long to him and he protected very well the ball, what he did on the first goal was class, his link-up play with Cazorla, but unfortunately he got injured.
"Wilshere sees a specialist tomorrow, finally, and we will know more tomorrow night. The specialist will decide [if he needs an operation]."
The Frenchman was pleased with his side's performance against the Bundesliga outfit, and insisted there was not much difference between this match and the loss to Manchester United.
"The focus [pleased me most]," he added. "Defending well together. We had a similar game to Saturday, we had to focus really well not to give any chances away and overall it was a committed game and maybe we were defensively better tonight.
"We are a team who likes to go forward and sometimes when you feel you dominate completely the game you are maybe a victim of that, and forget to take precautions to defend well but I think you learn from the games and we have done a lot better tonight."