Juventus midfielder Claudio Marchisio has been ruled out for between six and eight months after tearing anterior cruciate ligaments (ACL) while training with Italy.
Marchisio has returned to the Turin club after undergoing an MRI scan on Friday, and is likely to undergo surgery imminently.
The news comes as another setback to Juventus, who are without Paul Pogba for two months and are awaiting Andrea Pirlo's comeback from injury.
"Marchisio sprained his right knee," Italy national team doctor Enrico Castellacci was quoted as saying by the Italian FA's official website.
"An MRI scan was performed immediately at the Fanfini Institute in Florence, and this showed a partial ACL tear. It has been decided to send the player back to his own club for treatment."
On his Instagram page, Marchisio wrote: "Going home. As soon as I have confirmation about my situation I'll update you straight away. Thanks to everybody in the meantime! A hug"
A photo posted by Claudio Marchisio (@marchisiocla8) on
The 29-year-old has missed only one Serie A match all season, through suspension, and has been a mainstay of coach Massimiliano Allegri's midfield, scoring two goals and contributing six assists.
He has appeared in all but one of their Champions League games so far, helping them through to a quarterfinal against Monaco.