Manchester City defender John Stones face a lengthy spell on the sidelines after suffering an injury in Tuesday's 3-0 win against Young Boys.
City boss Pep Guardiola said the England centre-back is likely to be out for a substantial period following his half-time substitution at the Etihad Stadium.
Stones had already missed the first 10 games of the campaign with a hip injury sustained in pre-season before returning to action in October.
Asked if Stones would be out for a long time, Guardiola said: "Yeah, I think he will be out a while. I feel so sorry for him."
Stones' injury is a blow for Premier League leaders City, who face key matches against Liverpool and Tottenham after the November international break.
Adding to Guardiola's injury woes was the sight of Manuel Akanji suffering a back problem during the pre-match warm-up, with Kyle Walker a last-minute replacement for the Swiss defender.
The saving grace for City is their victory over Young Boys sealed qualification for the Champions League last 16, allowing Guardiola to rest players for their remaining two group matches.
"Manu had a problem in the back. Unfortunately John, he felt (injured) again," Guardiola said.
"It is a big loss for us. He is so important for what he does. He will recover, the season is long. He will be back stronger."