On-loan Bolton Wanderers striker Joe Mason has been ruled out for up to two months after tearing his hamstring.
The 23-year-old, who is on a season-long loan from fellow Championship side Cardiff City, picked up the injury in training last week.
"At this moment we're looking at between six and eight weeks, so we'll see how things develop and take it from there," Trotters boss Neil Lennon told the club website.
Mason has scored four goals in 12 Championship appearances this season, but had been struggling to get into Lennon's starting lineup prior to the injury - his last inclusion in the first XI was on October 25.
