St Kilda have revealed defender Hunter Clark will miss the start of the season with a fresh calf issue, while young midfielder Marcus Windhager is no certainty of playing Round 1.

Clark, who had exited AFL concussion protocols in the past week, sustained a calf strain at training on Monday that will require 4-6 weeks of recovery.

The ailment places the backman out of action until close to Rounds 2 or 3 at the earliest, adding to an interrupted start to the season for Clark who also recently suffered a facial fracture.

“Hunter had graduated concussion protocols and was reintegrating back into full-contact training,” St Kilda football boss David Misson said in a club update.

“Unfortunately, in a relatively innocuous moment of training, he strained his calf in a way we don't often see.

“While we'll have to monitor his progress, an injury like this could require a rehab period of 4 to 6 weeks.”

Windhager has required surgery after suffering a broken hand in last Frisay's practice game against Essendon.

Marcus Windhager and Harris Andrews during the round 22 AFL match between St Kilda and Brisbane on August 12, 2022 (Photo by Cameron Grimes / Zero Digital Media)

The third-year midfielder sustained a near-identical injury last pre-season on his opposite hand, with the club confident Windhager could be available for their season opener in mid-March.

“Marcus will be touch and go for Round 1, but we're confident this injury won't impede his availability much further beyond that,” Misson said.

“One silver lining is that Marcus is very attune to the best way to rehab this injury, so we're confident he'll get to work and be back as soon as he can.”

Two-time best and fairest winner Jack Sinclair is still in a race to be fit for Round 1 as he deals with his own calf issue, while midfielder Zak Jones has returned to full training after a recent concussion.

Paddy Dow (knee), Dan Butler (ankle), Jack Hayes (knee), James Van Es (ankle) and Ben Paton (pectoral) are all set to miss the start of the season, requiring at least three weeks of rehabilitation.

Neither Liam Henry nor Josh Battle are expected to miss any action after exiting last week's game early with separate issues.

St Kilda's season will get underway against Geelong at GMHBA Stadium on Saturday, March 16.