Benfica have fielded enquiries from Manchester United for Ezequiel Garay. United have asked Benfica to keep them informed of the Argentina defender's situation this season.
The Premier League leaders have scouted Garay three times in the last four weeks and Benfica officials accept a summer bid is likely.
Garay is viewed at United as a potential successor for Rio Ferdinand, who is off contract in June.
Real Madrid will have a say in any deal, with the Spanish giants having first refusal over their former player.