In-form midfielder Esteban Cambiasso has been ruled out for up to a month with a calf injury, leaving Inter Milan in trouble before their Champions League game with Sporting Lisbon on Tuesday. "We are now missing a man in the midfield," Inter assistant coach Sinisa Mihajlovic said on Monday. "With Cambiasso's injury we are in a state of emergency," he added in Calcio Italia magazine. The Argentinean picked up the injury during his side's 3-2 victory over Fiorentina in Saturday's Serie A opener. He was instrumental for Roberto Mancini's side as he scored twice and set up Zlatan Ibrahimovic for the third. Compatriot Julio Cruz is also doubtful for the Lisbon trip after sustaining a groin strain during the training on Sunday, Inter said on their website. Italy's double winners Inter play in Group B alongside Bayern Munich and Spartak Moscow.