Ipswich defender Damien Delaney will be sidelined for up to three months following emergency surgery to remove a blood clot.
The Republic of Ireland international sustained a dead-leg in training on Thursday and although he carried on playing the injury quickly deteriorated when he was later working out in the gym.
Town manager Roy Keane said: "It's a serious injury and he's a very lucky boy.
"He was lucky our medical care got him to hospital quickly and they operated straight away and then he had more surgery and we believe everything went well.
"Damien will probably be out for about three months. It's a big blow for us and a very serious injury."
Ipswich went down 1-0 to PSV Eindhoven at the Philips Stadium, with Danny Koevermans steering home from close range, while Town winger Luciano Civelli completed another half-hour as he works his way back from a knee ligament injury.