ROME, April 19 (Reuters) - AS Roma striker Francesco Totti may need an operation after suffering a knee ligament injury in Saturday's 1-1 home draw with Livorno, the club doctor said. The 31-year-old, hit by a series of niggles this term, was substituted after half an hour having tried for several minutes to shake off a knock. 'We must see if there is a partial or total lesion to the cruciate ligament, only then will we be able to decide if we operate on Totti or not,' Roma doctor Mario Brozzi told reporters. Second-placed Roma are three points behind champions Inter Milan in the race for the Serie A title. Coach Luciano Spalletti normally plays with only one striker and Montenegro's Mirko Vucinic, who scored on Saturday, looks poised to fill in for talisman Totti in their remaining four league games. Roma, the subject of a possible takeover bid, are also in the semi-finals of the Italian Cup.