Villarreal have confirmed striker Giuseppe Rossi will be out for six months after suffering cruciate ligament damage in Wednesday night's 3-0 defeat to Real Madrid.
Rossi was replaced after 60 minutes of the match at the Santiago Bernabeu and scans have revealed the extent of the injury.
A statement on Villarreal's official website read: "Worst fears have been confirmed. Villarreal's Italy striker Giuseppe Rossi seriously injured in his right knee in the match against Real Madrid at the Santiago Bernabeu and is out for six months.''
The club said the 24-year-old was set to undergo surgery on his his anterior cruciate ligament on Thursday night.
The news of the severity of the injury is a major blow to the Yellow Submarine, who have endured a dreadful start to the new Primera Division campaign.
Juan Carlos Garrido's side, who have become Champions League regulars, lie in the relegation zone with only seven points from their opening nine matches.
Rossi is perhaps the player they can least afford to be without. He scored 32 goals in all competitions last season and his form saw him linked with a move to Barcelona in the summer.
Villarreal are now seriously short of options in attack as their other senior striker Nilmar is also out with a knee injury for at least another month.
Italy coach Cesare Prandelli, meanwhile, has offered hope to Rossi by insisting the Villarreal striker remains in his plans for Euro 2012 despite suffering the injury.
"It's really bad news for him and for us,'' Prandelli told Gazzetta dello Sport. "But we will wait for him. All he has to do is to think of recovering with calmness. The day he returns to play then we will consider him.''
And Rossi's agent, Federico Pastorello, is confident his client will recover in time for Euro 2012. "Giuseppe is determined,'' he said. "There are still six months to go before the end of the campaign and almost eight months until Euro 2012.
"There is time for him to recover. I am certain that for the European Championship, he will be available.''