"It is a concern. Jamie has missed a lot of our pre-season and time is running out," said the manager.
"He really needs to be playing by Saturday if I'm going to be able to pick him for the QPR game.
"If he misses Bournemouth, it will be difficult for me to pick him.
"He's fallen behind the others and needs to gain that match sharpness that only comes from playing games."
McCombe played 55 mins against Forest Green last week but missed the matches against Yeovil and Swindon. He is suffering from sore shins.