Dundee United central defender Callum Morris suffered a medial knee ligament injury as the Tangerines lost 3-2 to Hearts at Tynecastle.
Morris was carried off just begfore half-time after being hurt in the run-up to the incident that saw his fellow defender Mark Durnan get sent off.
The early diagnosis is that he appears to have tweaked it rather than ruptured it and is looking at an absence of between three to six weeks.
United manager Mixu Paatelainen said: “It is his medial ligament he has tweaked that.
“So it looks like three to six weeks. That is the first diagnosis.
“Hopefully, it is less (time) but you get that in football.
“We will know more over the next couple of days.”
United finish the year 10 points adrift at the foot of the Premiership.
They got off to the perfect start against Hearts, scoring with Billy Mckay’s penalty after just a couple of minutes.
However, the hosts hit back and scored through Gavin Reilly, Prince Buaben and an Osman Sow spotkick.
Just before the break, Scott Fraser floated in a freekick to make it 3-2 only for Durnan to almost immediately get himself sent off.
Down to 10 men, they then lost Morris to injury and took off Mckay at the break in a tactical switch caused by Durnan’s dismissal.
Paatelainen added: “I thought it was an entertaining match.
“We didn’t defend at all well in the first half and gave them far too much room so I was very disappointed with that.
“The way we started the match was excellent and there was some very slick passing.
“I thought on a couple of occasions we looked very dangerous.
“It’s a pity but the goals we conceded were jokes again.
“We had a goal where the goalkeeper (Michal Szromik) parried (the ball) into his own net. We need to avoid goals like that.
“If we defend sloppily against Dundee this weekend they will punish us.
“I thought the effort the boys showed was excellent, as was the organisation when we were a man down.
“It was a pity that we had to make substitutions because of the sending-off and the injury because I felt that getting fresh legs up front would have helped.
“At least a point would have been nice but it wasn’t to be.”