Saints ruckman Rowan Marshall will miss the start of the 2021 AFL season with a stress injury in his foot.

St Kilda confirmed the unfortunate setback for the big man in a statement on Wednesday evening.

It is a big blow for the club just a month out from the season following hamstring injuries to speedster Zak Jones and Ryan Byrnes in recent days, while co-captain Jarryn Geary won't return to running for another five to six weeks with a fractured leg.

Saints Chief Operating Officer said the club would monitor Marshall's injury and not rush him back onto the field.

โ€œTo have this happen right before the season is obviously disappointing given Rowan is such an important player in our squad,โ€ย Lethlean toldย saints.com.au.

โ€œThese types of injuries are ones that you just need to monitor and take your time with, so weโ€™ll work closely with Rowan to make sure it continues improve so that he can return as soon as possible early in the season.โ€

Marshall enjoyed a breakout season in 2019 and backed up his impressive form last year even while sharing the ruck duties with Paddy Ryder.

The 25-year old averaged 14 disposals, 4.4 marks and 14.6 hitouts from 19 games in 2020.