THE SYDNEY Swans' tough trip to Perth to face Fremantle in Saturday's preliminary final just got harder with the news that Kurt Tippett and Tom Mitchell have both been ruled out.

Tough young midfielder Mitchell tore ligaments in the opening term of last Saturday's semi-final victory over Carlton and requires an operation, ending his season.

Tippett carried a slight knee issue into the game and came off second best in a marking contest with Michael Jamison in the opening minutes of the first quarter and was soon substituted out for Lewis Jetta.

Tippett would be a chance of returning if the Swans make it through to the Grand Final, but the club's leading goalkicker this week won't be lining up at Patersons Stadium.

"Mitchell is out. He needs an operation," coach John Longmire confirmed on Monday. "He's got torn ligaments in his ankle, so he's out for the season.

"Tippett won't play this week, he strained a ligament at the top of his fibula, which means he won't play this week as well.

"He felt it a little bit on Thursday and then ran fine on Friday, so we expected him to be fine going into the game.

"But obviously it didn't last long. A player fell across his leg in the first five minutes, which was the worst-case scenario for him and meant we needed to sub him.

"It was disappointing for him and us and he obviously misses this week."

The injuries add to a long list of sidelined Swans, including other tall forward options Sam Reid and Adam Goodes.

Lewis Roberts-Thomson made it through his first game time since way back in round four for the reserves on Sunday, but it could be too soon for him to be rushed back into the team.

Mitch Morton (knee) is also no chance of a recall, meaning the Swans are likely to have a smaller line-up to take on the Dockers.

Ben McGlynn (calf) is at least considered a strong chance to return, while Brandon Jack, Tony Armstrong and Jed Lamb are in the mix.

"The whiteboard will have another good working over this week and we'll have a look at what the team balance looks like," Longmire said.

"Our reserves had a good win yesterday and we'll get someone else to come in and fill those blokes' roles."

Rather than lament his ill fortune on the injury front, Longmire has been thrilled with the resilience his side has shown to still be alive this season.

The loss of Tippett means the coaching staff may need to alter the structure this week, as the underdone Roberts-Thomson is the only tall forward option they have left.

One player who could be close to his damaging best on the long Patersons Stadium is Jetta, who has pulled up well after being thrown into the semi-final much sooner than anticipated.

Following two weeks as a sub, Jetta could be part of the starting 21 this week.

"Lewis has pulled up really well, " Longmire said.

"To play 75 minutes and come out of the game feeling really good, that's a really good sign.

"If he'd played only a quarter on the weekend, we would've been discussing whether we play him in the 21.

"But the fact he got through 75 minutes of football and pulled up really well is a good sign for him."

While they will be underdogs this weekend, the defending premiers are also naturally ecstatic to still be in the hunt.

"We're one of four teams in the end playing in a preliminary final this week," Longmire said.

"It's a fantastic position to be in.

"There's a lot of other teams looking out this week that would love to be playing this weekend. We're one of them.

"It's not going to be easy, we know that, but what a fantastic opportunity."