Hull City defender Angus MacDonald will be out until at least March after a blood clot was found in his calf.
The former Barnsley and Torquay centre-back, 26, had been out with a calf problem since August and has now been diagnosed with deep vein thrombosis.
MacDonald, who has played 16 times for the Tigers since signing in January, will be on medication for four months.
"It was a big shock to find I have a blood clot in my calf, which will keep me out for a while," MacDonald said.
"The gaffer [Nigel Adkins], coaching staff and medical team have been brilliant in finding out the problem and getting to the bottom of it, as it could have been a lot worse."
MacDonald previously suffered from a blood clot on the lung at the age of 15, but made a full recovery.