ST KILDA will be without Rowan Marshall for at least a month with the ruckman set to undergo surgery on a plantar fascia injury that has plagued him for weeks.

Marshall was subbed off during Friday night's clash against Geelong after aggravating the injury, which also saw him miss the opening three rounds of the season, as well as round five.

MEDICAL ROOM The full AFL injury list

"This is a really frustrating injury to manage," St Kilda's chief operating officer Simon Lethlean said.

"It can seem a bit like one step forward, two steps back, but that is the nature of this issue.

"The only thing we can do is support Rowan and give him the time he needs to recover."

Midfielder Brad Crouch will undergo surgery on a fractured cheekbone during the week, but is expected to be ready for selection for round 10.