By Richard Clarke
Kolo Toure could be out for "three or four weeks at least" after picking up a calf injury in the goalless draw with Milan on Wednesday.
The Ivorian was injured after only seven minutes as he attempted to block Pato's drive.
Afterwards Arsène Wenger suggested the centre back's recovery would take some time.
"A calf injury rules him out for, from what I've seen after the game, for three or four weeks at least," said the manager.
Arsenal.com hope to have further injury news on Thursday afternoon.Copyright 2015 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source