Striker Steven Thompson has lost his fitness battle to be ready for Saturday's trip to St Johnstone and that could pave the way for new signing Stephen Carson to make his debut.
Thompson has been on the bench for the first two games of the campaign, but an ankle problem that first troubled him during the pre-season trip to Holland has flared up again.
"He's feeling some discomfort and rather than get him to soldier on, I think it is time to take him out for a week and give him the chance to recover," said boss Alex Smith. "His injury could open the door for Carson and he is in my thoughts. His fitness has improved as the week has gone on and he's been looking good."
The ankle knock Jim Paterson picked up at Motherwell last weekend is still causing some concern and he is rated 50-50 for the McDiarmid visit.