AS Roma's in-form right-winger Mancini will miss the return leg of the UEFA Cup first-round tie against Aris Thessaloniki FC on 29 September.
The 25-year-old Brazilian limped out of Sunday's 0-0 draw at AS Livorno Calcio with a thigh injury to his right leg and will be sidelined for about three weeks. "I'm very sorry for him because he was in great form," said coach Luciano Spalletti. Mancini is expected to return in time for the UEFA Cup group stage, should Roma qualify. The Giallorossi are in the driving seat after defeating the Greek side 5-1 at the Olimpico stadium last week.