A RELIEVED Alan Richardson initially feared Paddy McCartin's knee injury could have been "quite sinister".

McCartin, 21, will miss St Kilda's clash with North Melbourne on Friday night at Etihad Stadium, but could be fit to face Gold Coast the following week.

The St Kilda coach said at Sandringham on Thursday there had been concerns that McCartin suffered a stress reaction.

"At one stage yesterday, it looked like it was a chance to be something quite sinister, but the scans have come back relatively positive," Richardson said.

"We're quite optimistic now that it might only be the week. That's pleasing, (given) what it was a chance to look like."

The 2014 No.1 NAB AFL Draft pick has played three straight games since returning from a stint in the VFL.

He finished with a single goal in the 57-point loss to Adelaide last Friday but showed promising signs at the start of the game.

"He's had a bit of an issue with the bone in his leg, just below the knee," Richardson said.

"It might have been, early diagnosis, that he had some sort of real stress reaction there, but the scan's come back pretty positive.

"There's obviously still some bruising there and we think that will settle down pretty quickly."

A lack of continuity has impacted McCartin. He was concussed three times in 2016 and suffered a fractured collarbone in the penultimate round of the season.