Stefan Stam (pictured) could be out of action for the next four weeks after suffering damage to the cartilage in his knee. The 26 year old has only just returned to first team action and will need a knee operation, probably later today. It is thought that the injury was picked up in the recent encounter at Gillingham.Ronnie Moore said, “Stefan trained as normal at the start of last week, but then he had to pull out on Tuesday morning. I think he was trying to kid us (and probably himself) that everything was okay, but if you’ve got a cartilage problem, you’ve got a cartilage problem. We’ll have to see how long he’s out, but this is another chance for Marc Tierney to establish himself in the side. Marc just needs to steady down a bit and pass the ball with more care. We know defensively he can do a good job.”