The loss of key players towards the end of the season proved too much for the Swans to overcome in this year's finals series, coach John Longmire says. 

The Swans finished fourth on the ladder after the regular season but lost two straight games in the post-season to Fremantle and North Melbourne to finish 2015 in disappointing fashion.

With star forward Lance Franklin unavailable as he seeks treatment for a mental health issue, and reigning club champion Luke Parker (broken leg), co-captain Kieren Jack (knee) and Sam Reid (hamstring) all injured, the Swans were unable to keep their season alive against North in a 26-point defeat at ANZ Stadium.

Longmire said the unavailability of so many stars seriously dented the club's premiership tilt.

"We had some reasonable players out of the team, one or two that might go OK for us," Longmire said.

"We didn't want necessarily good luck we just didn't want so much bad luck towards the back end of the season.

"Every week there was something that bobbed up, we still showed some remarkable resilience but in the end ifs, buts and maybes don't count.

"We got the double chance and we still needed some things to go our way, some things didn't which was hard to get over in the end."

After making the Grand Final last season, consecutive defeats would have been hard for the successful Swans to take, but Longmire still believes his side is in premiership contention.

They've lost some significant experience with the retirements of Adam Goodes and Rhyce Shaw, but will be excited to see the development of youngsters like Isaac Heeney and James Rose in 2016.

"This year we won 16 games which is one off what we won last year, (when) we won 17 which is the highest in our history," Longmire said.

"We've got some good kids coming through and some of our best players, (Josh) Kennedy (is) 27 (years old), (Dan) Hannebery 24, (Luke) Parker 22.

"I looked out at one stage and we had (Isaac) Heeney, (Dean) Towers, James Rose, Tommy Mitchell, all in our front half, and it probably shows that we had some young kids that'll be better for that experience and are good young players, but were a little bit overwhelmed at times."

Speedster Lewis Jetta looks certain to leave the club in the trade period and will want to forget his last game in a Swans jumper, after being subbed out of the contest in the third quarter with just two kicks in his seven possessions.

The out-of-contract West Australian is believed to be heading back to his home state – with West Coast the front runners for his services – and left the Swans rooms visibly upset.

Longmire said Jetta's future is still undecided but he's been disappointed with the midfielder's form of late.

"Yeah the past few weeks we have (been)," Longmire said.

"He's played some good footy for us too, but his last few weeks have been quiet."