Mauro Camoranesi has suffered a dislocated shoulder during Juventus' 4-0 thrashing of Reggina yesterday.
Despite barely being able to move his arm, he insisted on carrying on and even scored the opening goal.
However, at half-time doctors were able to inspect it carefully and discovered he had dislocated it. He is expected to be sidelined until January.
Juve coach Claudio Ranieri said: "The doctor told me that the more he held his arm straight, the more painful it would be. We have a great rapport with Mauro and when he told me to wait, I believed he could carry on.
"We had discussed the fact Reggina were always compact and closed down the spaces, so we had to move the ball around quickly.
"The state of the pitch didn't help, but they were causing us problems by pressing us in midfield, so it was crucial to break the deadlock."