Adelaide's selection squeeze for their AFL semi-final against Collingwood was eased in unwelcome fashion on Wednesday by Nathan van Berlo's withdrawal because of injury.

But the ongoing saga of Nathan Bock's heel problem took another twist when he was able to run with minimal discomfort for the whole of the Crows' main training session, meaning he remains in calculations for the Saturday night final at the MCG.

Crows assistant coach Todd Viney said van Berlo's lower back flare-up, which had also ruled him out of last week's elimination final, was similar to a problem he had suffered early in the year, though on that occasion he had eased to full fitness inside a week.

"He is (a big loss)," Viney said on Wednesday.

"He's one of the leaders of the team and he's got a good finals record, so we were hoping he'd be right, but you never know with backs.

"He's just pulled up a bit tight in the middle of training and we didn't want to push him any further than that.

"Hopefully he can get himself right for next week."

Bock's promising training effort will force Adelaide's match committee to meet for a final selection meeting on Thursday once they have assessed his recovery from the mid-week session.

Viney grimaced noticeably when weighing up the options that must be considered for Bock, given the risk/reward proposition of picking an underdone player, irrespective of his quality.

"We were a little surprised last week that he got through the whole session but he pulled up a little sore after that," Viney said.

"Nathan thinks he's pulled up a lot better today, got through the whole training and looked probably better than last week.

"So the match committee have got some decisions to make with Bocky, whether we play him or whether he goes to the SANFL.

"Or we don't do that and give him another full week of training, it's such a hard decision.

"No doubt he's in our best team and All-Australian so we'd love him in there from a performance point of view, but we've just got to make a few decisions.

"We feel pretty confident that aerobically he'd be pretty good."

Tagger Robert Shirley trained well on Wednesday and will be in contention for a place against the Magpies, though Viney expressed confidence the 22 who lined up against Essendon had enough defensive cover to tackle Collingwood's varied attack.

Half-forward/midfielder Alan Didak was able to run riot at AAMI Stadium earlier in the season when not given a hard tag, but Viney did not guarantee he would be marked too closely this time around.

"He's certainly an important player," Viney said.

"Last week he had a pretty strong tag and Collingwood didn't play well, so was it because of that or more of a team effort.

"I'm a believer that if you have a good team performance you'll over-ride one or two players from the opposition.

"So the main point will be to make sure we have 22 contributors who get to their benchmarks again."

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