Arsenal manager Arsene Wenger has admitted he cannot put a timescale on when midfielder Jack Wilshere will return to action after suffering an ankle sprain.
Wilshere limped out of last Saturday's 2-1 defeat against Manchester United at the Emirates Stadium, with the 22-year-old's long history of ankle problems a cause of concern for Wenger.
"He has a big ankle sprain," he confirmed. "I don't want to talk about it because I'm not a specialist medically. The first news is we are told he will be out for the next few games. For how long, he will need to see a specialist."
Goalkeeper Wojciech Szczesny and winger Theo Walcott will join Wilshere on the sidelines for Wednesday's Champions League clash against Borussia Dortmund at Emirates Stadium, but there was better news for Wenger as defender Laurent Koscielny is set to return after a spell in the treatment room.
"He is in the squad for tomorrow," said Wenger of his French centre-back, who trained with his teammates on Tuesday. "It is very good news because he has been out for while now and defensively we are short in numbers. It is good to have his quality back."
Wenger suggested his side will face a tough challenge from Group D pace-setters Dortmund, despite a surprisingly poor start to the season in Germany for Jurgen Klopp's side.
"It is a quality team, with quality players," Wenger added. "They are quick going forward, defend all together. Individually, many of their players are international players for Germany, some for Poland. They are a very strong side.
"They had many injuries at the start of the season and after, because they are a big club and they get bad results, the questions come very quickly. Why do you lose? Then the confidence drops a little bit, but I don't worry too much for them in the championship [Bundesliga].
"They have a rival like Bayern that it is difficult to reach when you are many points behind. I don't think they will stay where they are at the moment."