Leeds United midfielder Kalvin Phillips is understood to be facing a lengthy spell on the sidelines.
The full extent of the damage is still to be determined but there are fears the 26-year-old could be set for an extended absence.
Phillips missed two games in October with a calf problem.
He is one of Leeds' most important players and it would be a major blow for coach Marcelo Bielsa not to have him available, with games against Chelsea, Manchester City, Arsenal and Liverpool coming up.
Leeds are still to reveal the extent of the hamstring injury that forced captain Liam Cooper off against Brentford.