AC Milan's suffered a blow as midfielder Giacomo Bonaventura was ruled out for the rest of the campaign following surgery on torn thigh muscles on Wednesday.

Italy international Bonaventura is one of Milan's key players and is expected to return to fitness "within four months".

"AC Milan announces that Giacomo Bonaventura was in Turku, Finland where he was operated on by Professor Sakari Orava, assisted by Milan medical chief Rodolfo Tavana," Milan said on their website.

"Professor Orava has expressed his satisfaction with the outcome."

Bonaventura is expected to return to competition "within four months notwithstanding complications."

The seven-time European champions have missed out on European competition the past few seasons and are currently seventh in the league table, 14 points behind leaders and champions Juventus.

Rossoneri hopes were compounded further last weekend when full-back Mattia Di Sciglio, also an Italy international, suffered ligament damage in his right ankle during a 2-1 loss at Udinese.