The Stamford Bridge-based outfit signed Matic in 2009 for £1.5million from Slovakian club MFK Košice before he was eventually sold to Benfica.
Matic spent just one full season at Chelsea before being shipped out on loan to Dutch side Vitesse on a season-long loan deal.
The 25-year-old was then transferred to Benfica in part of the deal which saw Brazilian international David Luiz complete a move to Chelsea.
And the west London club are now keen on re-signing their former employee as Chelsea boss Jose Mourinho is desperate to strengthen his midfield.
Matic reportedly has a release clause of £37million written into his contract, however Chelsea's bid of £20million could be enough to tempt the Portuguese side into selling their star midfielder.
Chelsea's Premier League rivals Manchester United and Manchester City were both said to have been interested in bringing Matic back to the Premier League, however it looks as if the Serbian could be heading back to London.
Manchester United are now likely to switch their attention elsewhere - with Koke, Ander Herrera and Ilkay Gundogan all said to be on David Moyes' wishlist.
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