Sydney Swans coach John Longmire has backed forward Lance Franklin to get better as his side prepares to enter the AFL finals without co-captain Kieren Jack.

Jack is expected to miss at least the first two weeks of the finals after being been diagnosed with medial ligament damage.

The midfielder suffered the injury to his knee in Saturday's night 63-point final round win over Gold Coast.

Swans football general manager Tom Harley said on Sunday the expected timeframe on Jack's return was three weeks. Swans football general manager Tom Harley said on Sunday the expected timeframe on Jack's return was three weeks.

"It is a really disappointing setback for Kieren and as our co-captain, he is clearly an important player for us," said Harley.

"He is the ultimate professional and will work closely with our medical staff to do everything he can to get himself right.'

Sydney go into that match on the back of four straight wins, all against teams who missed out on the finals.

Longmire expects utility Gary Rohan to play despite collecting a knee knock which forced him off the ground in the final quarter on Saturday.

He said Sydney's other co-captain, Jarrad McVeigh, was certain to face Fremantle after withdrawing on the eve of the Suns clash with a calf issue.

Longmire expected defender Nick Smith would be back in the frame after missing Saturday's game with a hamstring issue.

He said small forward-midfielder Ben McGlynn would also be in the selection mix after coming through a second straight game in the reserves.

The Swans have kicked 39 goals over the past two weeks, but Franklin has contributed just two of those since returning from a back injury.

He was substituted against St Kilda and struggled for impact against the Suns, tallying 13 possessions with six marks and kicked 1.1.

Franklin's sole goal was Sydney's 19th and last of the evening but he should have had two majors, as he missed his other shot into an open goal from around 35 metres.

"He trained this week fully, he needed another game," Longmire said.

"He'll train next week and play, so we think he'll get better as he goes." - AAP