He will be sidelined for another six months, ruling him out of Euro 2012 this summer.
"I wasn't able to talk to him for much yesterday, as Giuseppe did not want to contact anyone," agent Federico Pastorello told Sky Sport Italia.
"Today he seemed calmer. He has incredible character and great willpower, so this is a terrible blow, but he will overcome this too.
"It was a banal incident that caused it. He had been training with the team for three weeks and yesterday intensified his work to prepare for a friendly.
"In order to avoid a sliding tackle he jumped over his teammate and in falling felt pain. It is incredible that the same knee was so weak after surgery as to not hold up, so the cause has to be investigated thoroughly.
"He is angry, but also felt so much warmth from the people. For the first operation we allowed ourselves to receive advice from Villarreal, but now we will give priority to what Rossi wants."