Collingwood 2010 premiership forward Alan Didak has torn an adductor muscle in his groin and will miss at least four weeks of training.

The 28-year-old left-footer had scans late yesterday which confirmed a tear after he injured himself at training.

Collingwood's director of football Geoff Walsh said the length of Didak's absence was unpredictable.

"It could ebb and flow as he progresses or otherwise through the treatment. It's not catastrophic but its obviously not something he or I would want."

Didak struggled for form in 2011 after missing much of pre-season due to a severe injury to the pectoral muscle in his arm. He then suffered a calf injury which cost him five matches mid-season. The skilled small man managed to play 20 games, but was down hugely in every statistical category, and had little offensive impact, failing to boot a goal in his last nine games.

"The way the game is today it's too unforgiving to be able to miss big slabs of time in pre-season through injury," Walsh told SEN radio this morning.

Walsh said the dual All-Australian had not experienced any previous issues with his groin.

Apart from Didak's setback, the Magpies' 'injury profile' is good, says Walsh. "In a general sense, guys who have come back from medium to long-term stuff like Nathan Brown and Ben Reid … are progressing quite well."

He expects Irish utility Martin Clarke, who returned to the Magpies after two years at home, to push for an immediate reinstatement in the Collingwood line-up, saying the prospective flanker or midfielder was in “good nick” and doing well in aerobic testing.

"I think a lot will depend on his NAB Cup form. I'm sure that because of the format of the NAB Cup that he will get an early opportunity in some of those games.

"So then it becomes a situation of someone gets in and they do well, then someone has to get them out, It won't surprise if he's going to be around the mark round one, for sure."