Arsenal manager Arsene Wenger has revealed Mikel Arteta sustained a severe ankle injury during the Gunners' 2-1 defeat to Wigan Athletic on Monday night.
The midfielder had to come off during the first half and Wenger said that the problem was a "serious one" immediately after the match.
The Frenchman told Sky Sports: "He had to come off. It's an ankle problem. It looks quite a serious one.
"We have to scan it tomorrow, it's too early to say tonight. But it doesn't look like a little ankle sprain. It is a serious one."
The 62-year-old manager was disapointed with the way the second goal was conceded, especially as his side were not able to field a replecement quickly enough.
He continued: "We defended horrendously on the first and second goal, everyone included. On top of that, we conceded the second goal with 10 men on the pitch. It took us too much time to change, that was absolutely unbelievable. We concede the first goal with Arteta out, and we can't even put the player on because he's not ready."
"When a player is injured, if he stays on the pitch you have time to bring [the sub] on. It was a misunderstanding, but the moment he walked off, Ramsey was not ready. The players think that in the first half they do not come on, so he was not ready. Basically we played with 10 men which should not be the case when the player is injured."
Wenger also expressed his annoyance at Wigan's time wasting towards the end of the game, Ali Al Habsi's picking up a yellow card as his side did all they could to hold on to victory.
"You know what, I told the fourth official [Al-Habsi] will [time waste] the whole game, because he did it after 10 minutes. And with three minutes to go he gets a yellow card. Exactly what happened. That's why I went to see [the fourth official]. I predicted what he would do, and that happened. It's not serious, frankly. It's disrespectful to people who watch the game and pay big money to watch the game. But we didn't play well. We are sorry. That the referees do not act on that is not right.
"I do not want to use excuses. I congratulate Wigan, they did well. But the referee has to give him a yellow card the second time he does it. Either for us, or for somebody else it's exactly the same. When the ball goes out on the right, it's a goal kick on the left [and vice-versa]. I can understand that they do it, but it's time for the referee not to allow it."