SL Benfica striker Mantorras could be out for the rest of the season after a knee operation on Monday.
Club doctor Bernardo Vasconcelos said that the Angolan international will be out for at least "four or six weeks" following surgery on his right knee.
Mantorras, who will be 20 on 18 March, joined the Lisbon club last summer from FC Alverca and has scored ten goals in 23 games.
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