Sydney midfielder Kieren Jack's night has ended early, the former co-captain injuring his left knee in the first quarter against Geelong.

Jack attempted to tackle Gary Ablett early in the opening quarter of the clash between the top-eight sides, appearing to injure his medial ligament.

The 31-year-old had his knee strapped and attempted to warm-up on the sidelines but failed to make it back on to the field.

Swans' head of football Tom Harley told Channel Seven at quarter-time Jack was ruled out of the remainder of the match.

"It looks like a medial, so he won't play anymore," Harley said.

"It was a contest down at centre half-back, so disappointed for him and for us."

Jack later told Channel Seven he would get scans on his knee on Friday morning.

"I did [a medial ligament] a few years ago, felt pretty similar, I just felt a click in it," Jack said.

"I think it's on the minor side. We did some tests on it and it's classic medial symptoms, so without taking the risk, we pulled the pin.

"I'll get a scan first thing in the morning just to check on it and we'll go from there, the docs and physios will let me know. I'll probably miss a little bit of footy, I would have thought."

Late in the final quarter, fellow veteran Jarrad McVeigh came from the field holding his right collarbone following a tackle, and took no further part.