St Johnstone are likely to be without Frazer Wright for at least a month after the defender tore a calf muscle.
Wright limped out of Tuesday's League Cup loss to St Mirren and joins a long injury list at McDiarmid Park.
"At best we are looking at him being out for three weeks, at worst it's six weeks," said manager Derek McInnes. "It will probably be somewhere in-between.
"I'm disappointed to lose him, he has played every game for me and he's got a big presence."
St Johnstone, who picked up former Kilmarnock man Wright on a free transfer over the summer, have a long injury list to contend with.
"We were really keen to bring Frazer in and now that he's out it's a bit of a blow," added McInnes.
"We are fortunate that we have got David McCracken back fit just at the right time but we have got just a few too many injuries for my liking to a lot of our key players. We'll just have to get on with it."
Jody Morris, Kevin Moon, Sam Parkin, Callum Davidson, Graham Gartland and Murray Davidson are the other first team regulars on the sidelines.