LANCE Franklin has resumed running as he tracks toward an uncertain AFL return date, with Sydney coach John Longmire declaring the club won't let the injury-plagued superstar play until it is confident he can back up.

Franklin hasn't played since celebrating his 300th game in the final round of the 2019 season, which itself was a comeback match some two months after suffering a hamstring strain.

The four-time Coleman medalist's latest concern is a sore calf, which has put him in doubt for the Swans' season-opening clash with Brisbane on March 20.

Franklin was an invested onlooker at Thursday's intra-squad game, continuing to mentor the young teammates he travelled with throughout a 2020 season spent mostly in hubs.

"He'd had some good solid training up until two weeks ago, when his calf tightened up. He ran yesterday, ran quite well, he'll run again tomorrow," Longmire said.

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"He's been doing everything right and then some, which has been great to see."

Longmire noted "miles in his legs" was the main box 34-year-old Franklin, whose nine-year deal runs until the end of the 2022 season, must tick before being cleared to return.

"The only apprehension is we just need him to train enough, to be able to get resilient enough to play ... to feel confident he can play. Not only one game, but game upon game," he said.

"It's not about just seeing him jog around and have a kick, then hopefully things work out well."

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Captain Josh Kennedy also sat out Thursday's scratch match because he had a sore back last week but Isaac Heeney took part and impressed as the Swans continue to increase the young gun's workload.

Heeney underwent major ankle surgery last year, when Sydney sorely missed him and a stack of injured stars.

The absence of Franklin, who requires 56 more goals to become just the sixth player in VFL/AFL history to join the 1000-goal club, was particularly glaring.

The Swans ranked 16th in average goals last season, finishing in the same spot on the ladder.

"Part of the development of our team is working without him," Longmire said.

"We've introduced (No.4 draft pick and key forward) Logan McDonald, made some changes in our front half because that's what we needed to do.

"If Lance isn't there, he's not there, we need to work our way through it."

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Longmire expressed excitement about Sydney's youngsters, adding they had benefited from greater opportunities in 2020 because of the club's injury crisis.

"One of the real positives we got out of that season was the development of that younger group," he said.

"We exposed a number of players last year ... especially through the midfield."