Ghana's Sulley Muntari faces a race against time to be fit for Sunday's crucial Milan derby after pulling up during training on Wednesday with a thigh injury.
The setback was confirmed by his club, Inter Milan.
Muntari's loss adds to the lengthy injury concerns for Jose Mourinho who is without Samuel Eto'o on Africa Cup of Nations duty.
Already three players - Thiago Motta, Dejan Stankovic and Rene Krhin - are all struggling to be fit for the match that will see the top two in Serie A clash at the San Siro.
Inter are top of the table with a six point lead over Milan, although their opponents do have a game in hand.
Earlier in the season Inter handed out a 4-0 drubbing to Milan.
