The Juventus utility man sustained a muscle injury in his left thigh during training last weekend and will need at least two weeks to recover.

"If everything goes well, he will come back in 15 to 20 days," said Italy team doctor Enrico Castellacci.

"In a week's time, he will have another test done but we are calm and optimistic."

Zambrotta, who is a regular member of Marcello Lippi's squad, could recover in time to face USA on June 17.

Although doctors have ruled out a ligament damage, Zambrotta will need to have a scan and is unlikely to travel to Geneva with the rest of his team-mates for the warm-up friendlies against fellow World Cup qualifiers Switzerland on Wednesday and Ukraine on Friday.

There was more bad news for Lippi on Tuesday with Roma midfielder Simone Perrotta unable to finish training having picked up a knock on his right knee.

The clash in Geneva will allow Lippi to test the fitness of some of his players.

However, Lippi is set to rest Roma captain Francesco Totti, who recently recovered from a serious leg injury.

"Totti is improving and he is undergoing specific training to gain more strength in his injured leg," said Lippi.

AC Milan's Andrea Pirlo is favourite to replace Totti at the heart of Italy's midfield with Roma's Daniele De Rossi set to be relegated to the bench.

Against Switzerland, Italy will play with a 4-3-3 formation, with Alberto Gilardino, Luca Toni and Alessandro Del Piero set to form the Azzurri's attacking line.

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