Inter Milan left back Cristian Chivu is in hospital after fracturing his skull in a clash of heads during Wednesday's 1-0 Serie A win at Chievo.
The Romanian's life is not in danger but he will have to stay under observation for some time.
"He is in hospital, he has a fractured skull and we hope he can come back as soon as possible but I think he will be out of action for a while," Inter coach Jose Mourinho told Inter's TV channel.
Chivu was immediately operated on and the medical team are confident the two-hour procedure went well.
"The player suffered a head injury in the right parietal region,'' said surgeon Sergio Turazzi. "The trauma caused inward fractures of the skull and bleeding, and a haematoma of limited size.
"The operation was necessary mainly because of the presence of this haematoma and consisted of raising the bone fragments which had sunk towards the brain, of draining the haematoma and creating conditions so that the haematoma does not reform. The surgery went well.
"The brain walls appeared undamaged, the cranium was reconstructed with the bone of the patient and regained a normal profile. Everything went well and so we are quite confident that the patient can heal without any problems. It is too early to say when the patient can leave hospital.''
The loss of Chivu is a blow to the Serie A leaders, who have no like-for-like replacement. Inter's right-footed full back Davide Santon is also injured.
Media reports said Inter were chasing Lazio left back Aleksandar Kolarov even before Chivu's injury but Lazio president Claudio Lotito has said the Serbian is not for sale.
Mourinho, who has already brought in Macedonia forward Goran Pandev, also hopes the club can recruit another midfielder in the January transfer window with the little-used Patrick Vieira on the verge of leaving.