THE SYDNEY Swans will look to keep their season alive in next Saturday's cut-throat semi-final without key forwards Lance Franklin and Sam Reid.

Franklin missed Saturday's qualifying final loss to Fremantle at Domain Stadium after it was revealed during the week he was battling a mental illness.

The Swans have not put a timeframe on a return for the star forward, with coach John Longmire immediately ruling him out of the semi-final against the winner of Sunday's North Melbourne-Richmond clash.

Six talking points: Fremantle v Sydney Swans

To add further salt to the Swans' wounds, Reid injured his right hamstring in the second quarter of the qualifying final and was subbed out immediately.

After the game, Longmire was resigned to the fact Reid would likely miss the rest of the Swans' finals campaign.

"It looked like a bad one, but we haven't had a scan yet," Longmire said after the loss.

"He'll be out for a few weeks I'd imagine."

Click here to watch John Longmire's full media conference

With Reid subbed out of the game, young forward Dean Towers stood up across centre half-forward.

In his 10th senior game this season, the 25-year-old finished with 15 disposals, seven marks (two inside 50) and kicked 1.2.

"He was terrific," Longmire said.

"He's powerful, he's quick and he was probably a bit stiff earlier in the season being in and out of the team. When he's been given his chance, generally he's taken it.

"He was fantastic and really ran hard today. Once Reidy went off he was our centre half-forward and led and presented and really gave our midfielders an option."

In good news for the Swans, Longmire said defender Nick Smith was a "big chance" to return for the semi-final, while young gun Isaac Heeney should be available to play after receiving a knock to his shin early in the game.