Derby midfielder Paul Green has undergone knee surgery which could keep him out for the remainder of 2011.
The Republic of Ireland international ruptured the anterior cruciate ligament in his right knee during the defeat at Cardiff at the start of April and had an operation in London on Wednesday.
Green had to wait until this week for the reconstruction procedure due to the swelling in his knee.
Derby physio Neil Sullivan told the club's official website: "The surgeon was very happy with the result of the operation and Paul will start his rehabilitation work immediately."
It is thought Green will return to fitness towards the end of 2011 or early in 2012.