Azzurri boss Cesare Prandelli has said he hopes the AC Milan forward, a key member of the national side, will be fit for the tournament in Poland and Ukraine in which Italy's first game is in Group C against holders Spain on June 10.
However, Cassano, 29, sounded more cautious when interviewed by Italian television on Thursday.
"It was a shock. The important thing was to get back to daily life. I'm going to have to wait six months to play. In the meantime, I walk, walk, walk," he said.
Fellow Italy forward Giuseppe Rossi is also out with a long-term knee injury and is racing to be fit for Euro 2012.
Prandelli said this week he would call up veteran forward Antonio Di Natale to play alongside Mario Balotelli in February's friendly against the United States.
Italian champions Milan are trying to bring in Carlos Tevez from Manchester City to fill in for Cassano in the second half of the season with Serie A, the Champions League and Italian Cup still up for grabs.
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