Rangers midfielder Niko Kranjcar will be out of action for the next six months after suffering cruciate knee ligament damage, manager Mark Warburton has said.
The 32-year-old Croatian suffered the injury in training last month and medical checks have confirmed the serious nature of the problem.
Warburton said: "Niko has unfortunately suffered an ACL injury. He's currently having it reconstructed by one of the best surgeons down in London.
"It will be a six-month rehabilitation period for Niko. Everyone in the building is so disappointed for him. They know how hard he works."
Former QPR, Portsmouth and Tottenham player Kranjcar joined Rangers on a two-year contract in the summer.
Rangers could seek a short-term replacement.
Warburton said: "We might look for a loan option in January. We need to have strength and depth. We'll see how the squad is shaping up come then."