The 25-year-old formed part of the deal that saw David Luiz arrive at Stamford Bridge in a player-plus-cash deal in January 2011, and has gone on to establish himself as a star man at Estádio da Luz.
His impressive performances have caught the eye of Jose Mourinho, who is keen to bring Matic back to west London ahead of the 2013/14 campaign.
Mourinho is understood to have convinced Russian owner Roman Abramovich to bankroll a move for the Serbia international, who signed for Chelsea from Slovak side Kosice for a comparatively small £1.5million fee just four years ago.
Benfica are determined to keep Matic in Portugal, and so will demand a huge fee for his services, in an attempt to deter their Europa League final opponents.
Big-spending Ligue 1 side Monaco have also been credited with an interest in the player, with the Daily Express reporting that former Chelsea boss Claudio Ranieri is ready to meet Matic's £42.4million release clause in order to entice him to France.
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