Manchester City striker Mario Balotelli pulled up in training with Italy ahead of their Euro 2012 qualifier with Estonia on Friday.
The 20-year-old suffered a sprain to his right knee, confirmed by the Azzurri's team doctor Enrico Castellacci:
"Balotelli suffered a relapse of the pain in the right knee that had already troubled him in the past," Castellacci told the Italian press.
"It was a small sprain of the right knee. It'll be difficult to get him back by Friday, so he's unlikely to recover in time to face Estonia.
"Between today and tomorrow we will evaluate whether to keep him in the squad or send him home," he concluded.
Balotelli was injured in a practice match against Italy's Under-18 side, and now remains a doubt for the international friendly against the Republic of Ireland next week.