Young St Kilda key forward Paddy McCartin has been ruled out of this weekend's round of matches following a concussion he suffered in the VFL last Saturday.

McCartin copped a head knock in the opening quarter of Sandringham's loss to Coburg last weekend, and won't play at either the VFL or AFL level with the club taking a cautious approach towards the forward.

“Paddy unfortunately copped a head knock in the first quarter and was ruled out of the game,” Saints GM Football Performance Jamie Cox told saints.com.au.

“Paddy has subsequently been taken out of this week – he hasn’t quite recovered in time.

“We’re hopeful that he will be available for next week. He will be tested early next week to try and progress him towards that.”

It's McCartin's first head knock of 2017, after the forward sustainted three concussions over the course of last season.

Cox also provided an update on injured star David Armitage, and suggested the 29-year-old is still up to a month away.

“Dave has started running and is training well,” he said.

“He’s probably still four weeks away from returning to footy but it’s encouraging to see him running laps of the oval here at Seaford.”