Italian sports daily La Gazzetta dello Sport reports the 21-year-old missed Wednesday morning's training session after suffering the problem on Tuesday and left team's training camp in Coverciano to undergo further tests in a nearby hospital.
Balotelli's injury is a further setback for the Italians, who are already without Inter Milan forward Giampaolo Pazzini (foot) and are sweating on the fitness of Villarreal frontman Giuseppe Rossi (knee).
AC Milan's Antonio Cassano and Parma's Sebastian Giovinco are currently Italy's only fit strikers for Friday's game in Belgrade, and coach Cesare Prandelli may be forced to call up a replacement.
Source: Team Talk
Source: Team Talk