GEELONG defender Aaron Black may face an extended stint on the sidelines, with the club fearing he has torn the anterior cruciate ligament in his left knee.

Black appeared to badly hyper-extend his knee while landing in a marking contest during the third quarter of Geelong's 37-point win over North Melbourne.

"Unfortunately, this doesn't look good for Aaron," coach Chris Scott told Fox Footy on Monday night.

"I had some misplaced confidence post-game, and I must admit when I saw it, I thought the worst. He was up and about and moving, and there was some hope post-game, but it looks like it's an ACL injury of some description.

"Whether it requires surgery, and exactly what that procedure's going to be, we're not quite sure yet."

Black, who generally played forward for his old side North Melbourne, has run out seven times for the Cats since joining them in 2017.

The 27-year-old had managed three senior games in a row before this latest injury setback.

"It's devastating for him, clearly. I spoke to him yesterday and he's still pretty upbeat, he's that sort of guy," Scott said.

"I can't be any more sincere when I say the whole footy club, and even North Melbourne, really feel for him. He's just a great clubman. Post-game, there was a suspicion he had done an ACL and he was out on the fence signing autographs for kids. 

"If anyone has any right to feel sorry for himself it's Aaron, and he hasn't shown any sign of that, so it's disappointing. We have to find a way to stick by him."

If Black does not require surgery, there's hope in an example from earlier this year.

Western Bulldogs veteran Dale Morris partially tore his ACL in February, did not require surgery, and after an extended period of rehabilitation and strength training, returned to the senior side in round 11.