St Mirren boss Danny Lennon is '95 per cent' sure that Darren McGregor has suffered the second cruciate ligament injury of his career.
The defender was carried off during the Saints' 2-1 defeat to Hibernian in the Scottish Premier League on Saturday.
McGregor was out for seven months with cruciate ligament damage sustained in his other knee a year ago.
Lennon told the club's website: "Darren had a scan on his knee today (Monday) and we are now waiting on the full report.
"That being said we are 95% - although we await confirmation - that he has damaged his cruciate in the other knee from the one that was injured last season.
"It's a big blow for all concerned - for Darren, the club and the fans."