Manchester United legend McIlroy said: "Sol hasn't played a competitive game since May, and I hope he hasn't been cutting any corners in his training.
"He is going to have his hands full with Mullin and if Sol is a bit rusty or off the pace he will get exposed.
"I brought Mullin in from Accrington just before the transfer window to give us a bit more presence up front. He is a gritty, no-nonsense type of centre-forward - a throwback to the old days.
"He will not have too much respect for Sol's reputation - in fact he will see this as a chance to make a bit of a name for himself."