Suspended midfielders John Rankin and Willo Flood have joined long-term injury victims Johnny Russell and Gavin Gunning on the sidelines ahead of the visit of Clydesdale Bank Premier League bottom club Dundee.
And captain Jon Daly and defender Brian McLean are both struggling to make the Tannadice clash.
McNamara knows the situation is far from ideal but he urged whoever is handed the chance to seize the moment by staking a claim for a regular starting slot.
He said: "It's not looking great squad-wise for the derby.
"A couple of youngsters could be thrown in because of that.
"I would say Jon is more doubtful at the moment than Brian because of his groin. Brian came off against St Mirren last weekend with a wee tweak to his hamstring.
"So hopefully he might have a chance of making Sunday but it will be a last-minute decision. It's about getting the right balance with the squad that's important.
"We seem to be getting hit in certain areas of the team."