Ryan Taylor is facing up to 12 weeks on the Newcastle sidelines after undergoing surgery to repair ankle ligament damage.
Boss Chris Hughton revealed last Thursday that Taylor had suffered an ankle injury in training, but the extent has only just been revealed.
He underwent surgery on Monday and is expected to be out of action for up to three months.
Hughton said: "It's very disappointing to lose Ryan for this period of time.
"Although he hasn't played as much football as he would have liked, he has been a very valuable member of our squad this season."
It is understood that Taylor was injured in a challenge with team-mate Sol Campbell.
The 26-year-old has made only four appearances to date this season, with his three starts all coming in the Carling Cup.