ST KILDA'S tall forward stocks have taken another hit, with untried youngster Matt Allison needing surgery on a stress fracture in his left foot, ruling him out for up to five months.

Allison had been impressing over pre-season as a potential replacement for Max King, who is set to miss the first month of the season with a shoulder injury.

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The 20-year-old came second in the Saints' time trial after the Christmas break, with his contested marking also a highlight at training, but will need time off to deal with the issue in his navicular bone.

"Matt had really been impressing on the track, so for this to happen is very disappointing," St Kilda performance, medical and operations manager David Misson said.

"Following consultations with specialists we elected to send Matt in for surgery to have the foot stabilised. 

"While the recovery time is 16-20 weeks, which is significant, Matt's a really positive and professional young man.

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"He goes into this period of rehabilitation with the whole club behind him."

Allison was selected with pick No.26 in the 2020 NAB AFL Draft from Calder Cannons.

The Saints are already down a tall after the retirement of Paddy Ryder, while Tom Campbell (Achilles) suffered a setback before Christmas. Jack Hayes is rehabbing a ruptured ACL, suffered in round six last year, and also needed foot surgery earlier this month.

Former Essendon key-position player Josh Eyre has been looked at by the Saints as a potential pre-season supplemental selection period.