Substituting Swans spearhead Lance Franklin out in the third quarter against St Kilda was planned pre-match, coach John Longmire says.

After spending three weeks on the sidelines due to a back strain and rib cartilage damage, Franklin kicked one goal from seven disposals before being whisked off – much to his bemusement – at the 10-minute mark of the third quarter.

Longmire insisted the move did not indicate a fresh injury to the superstar forward. 

However the Swans are uncertain on the status of All Australian defender Nick Smith, who left the field with a hamstring injury in the third term of the club's 97-point thumping of the Saints.

“The aim was to get [Franklin] off halfway through the third and bring Gary (Rohan) on," Longmire said.

"We were a little bit unfortunate that Nick got injured or didn't play anymore five minutes after that but as far as planning it, it went the way we wanted it to."

Longmire said the Swans took the "cautionary route" with Smith, although are unsure if he will be available for the Swans' clash with Gold Coast next Saturday night.

"His hamstring tightened up. It's only minor so we don't know," Longmire said.

"We went the cautionary route and we hope it's OK.”

Longmire said it was imperative for the Swans to get as much game time into Franklin as possible leading up to the club's finals campaign.

"He usually comes to hand pretty quick, so that's why it was important for him to play tonight," Longmire said.

"He trained this week but we wanted to get some game time into him tonight and he'll need it again next week; so the plan will be to play him the full game next week."

While Franklin looked sharp, it was left to Isaac Heeney (four goals), Kurt Tippett (three) and Adam Goodes (three) to hit the scoreboard as the Swans slammed home 20 goals.

The midfield also fired with Dan Hannebery, Tom Mitchell, Josh Kennedy and Kieren Jack racking up 136 touches between them, while the contested possession count was heavily slanted the Swans' way (149-116).

The Swans now need to defeat Gold Coast at the SCG next Saturday night to be assured of a spot in the top four and hold their one-game lead over a charging Richmond.

Should they succeed a qualifying final showdown with Fremantle in Perth awaits.

"You want to get to this point of the year where you control your destiny as far as where you want to finish in the top four," Longmire said.

"It's a big challenge to get there and we've got one game to go next week and we don't want to rely on percentage.

"We've still got a bit of work to do."

However, Longmire said the side was far from settled with Jake Lloyd, Dean Towers, James Rose and perhaps Ben McGlynn (hamstring) and Craig Bird still in the selection mix.

"We need a squad of players at this time of year and we need to make sure those blokes are playing really good footy," Longmire said.

"You're never quite settled."