The Gunners were denied by three points by a late penalty against West Bromwich Albion on Sunday, with Arsene Wenger's woes exacerbated by the loss of two key defenders to injury. Kolasinac was forced off after just 37 minutes following a heavy challenge from Baggies midfielder Gareth Barry, while Koscielny was taken off in the second half.
Speaking at a press conference on Tuesday, Wenger confirmed the former Schalke defender is now facing at least a fortnight on the sidelines, with Koscielny unlikely to return in time for the visit of Antonio Conte's side.
"[On Koscielny] yesterday the medical staff were pessimistic. He is 30% available, 70% not available. Kolasinac is out completely for at least two weeks," Wenger said.
"We dedicate our time to recovery. We work a little but today for preparing for tomorrow's game. Basically it is 80% recovery, 20% training. We have a squad equipped to deal with that, we have proved that in the Europa League, but we cannot lose any more players now because we are a bit a short."
Ozil, meanwhile, sat out of the draw at the Hawthorns after picking up a minor knee problem. The Germany international is still being assessed by the club's medical staff and is yet to return to training.
"Ozil has a little chance," Wenger added. "He has a test this morning, but he has not been out [training] at all since Crystal Palace [on 28 December]."
With doubts over Ozil and Koscielny and Kolasinac ruled out, Arsenal could be without seven members of their first team for the meeting with the Blues. Aaron Ramsey remains sidelined with a hamstring injury while Nacho Monreal is still recovering from an ankle injury suffered in the clash against Liverpool before Christmas.
Olivier Giroud, meanwhile, sustained a hamstring issue in the Carabao Cup quarter-final victory over West Ham United, while Santi Cazorla remains a long-term absentee.