Derby manager Nigel Clough has revealed that Paul Green and Jake Buxton could both be sidelined for some time.
Midfielder Green has been hampered by a foot injury in recent months and missed Tuesday's 3-2 defeat to Barnsley after the problem flared up again in training.
He may now require more surgery, having gone under the knife last season to repair a broken metatarsal, and Clough fears he will be out of action until late October.
"We are not quite sure what the diagnosis is but he may need an operation and we could lose him for four to six weeks," Clough told the Derby Evening Telegraph.
"There is obviously something that's not right with his foot.
"We were advised by the specialist that if Greenie rested his foot during the international break, it would be fine. He played against Sheffield United and then a few days later he started feeling it again.
"So something is not right and we will have to investigate it further."
Clough will also monitor the fitness of Buxton but it is thought the defender could be out for a few weeks as well.
"Jake's got a problem with his stomach, it could be a hernia," explained the Rams boss. "We will have it checked out."