Arsene Wenger has delivered bad news regarding injured captain Mikel Arteta.
The Spaniard was withdrawn against Borussia Dortmund, and Wenger did not sound positive after the game.
He told SkySports: "It doesnt look good. It's a calf.
"We've go to take it on the chin. At the moment we play many games and we need everybody available. I think Arteta, he will be out for a while."
Manchester United striker Radamel Falcao has just missed a month with a calf injury, and if the Spaniard were to have the same sort of lay off time it would be a big blow.
Arsenal's upcoming fixtures are away to West Brom, at home to Southampton, away to Stoke and away to Galatasaray.
The Gunners have just lost Jack Wilshere, who even if scans are positive on his injured ankle, will be out until at least January.