Xhaka has missed three games since suffering an ankle injury in the home victory over Crystal Palace, but there was hope he'd soon be ready to return after Le Bris revealed at the end of last week that the captain was back running on the treadmill.
But after Saturday's defeat to Arsenal, Le Bris confirmed it's still unclear when the midfielder will be ready to return, with the head coach admitting the 33-year-old could be out for another three weeks.
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He will definitely miss the visit of Liverpool in the Premier League on Wednesday night and next week's FA Cup trip to Oxford, and looks likely to be out for the home game against Fulham on Sunday, February 22. If Xhaka does need three weeks to recover, he'll also be a major doubt for the trip to Bournemouth on Saturday, February 28.
"We don't know yet," said Le Bris on his captain.
"Probably two or three weeks. We'll see according to his feeling and just wait a bit."
There was better news on the fitness front, with Le Bris revealing Noah Sadiki should be OK to play against Liverpool on Wednesday night, despite suffering with a minor issue in the second half against Arsenal. He was replaced with 20 minutes to play.
Le Bris said: "I think he'll be OK. He struggled a bit with a bit of discomfort."