The 25-year-old spent two years with Chelsea before leaving in 2011 in the deal which brought David Luiz from Benfica.
Matic has since emerged as one of the top midfielders in Europe and now he is in line for a move back to Stamford Bridge.
Reports in Portugal claim that Chelsea will pay around £25million for the Serb, and also send winger Gael Kakuta to the Estadio da Luz on loan.
Matic has now confirmed that the weekend win over Porto was his last game and told A Bola: "The game against FC Porto was my last game for Benfica.
"I want to thank everyone at the club and all the fans. Benfica will forever be in my heart.
"I played here for two-and-a-half years, gave my best at every training session, and now it is the right moment to leave.
"I want to improve, I want to play in a better league and I want to go to Chelsea, a club I also love.
"I would also like to thank Benfica's president, he did everything he could to keep me, but I wanted to leave.
"I insisted on leaving because I think this is the right moment."