Arsene Wenger has admitted that Arsenal cannot afford to lose any more players to injury after being dealt a double blow against West Bromwich Albion.
Wenger says that Kolasinac will definitely sit out Wednesday night's meeting with Chelsea, while Koscielny and playmaker Mesut Ozil - absent for the 1-1 draw against West Brom at the weekend - have an outside chance of featuring.
"At the moment our injury list is quite long. We lost Kolasinac, Koscielny in the game at West Brom," he told reporters. "The two who have a little chance are Ozil, who might have a test this morning and Koscielny, who is 30-70 available.
"We have a squad that is equipped to deal with injuries - we've shown that in the Europa League and the Carabao Cup... but we cannot lose any more players now."