Sky sources understand that Nemanja Matic is expected to complete his return to Chelsea today.
The 25-year-old midfielder left Chelsea in 2011, but has travelled to London ahead of a £25million return to Stamford Bridge and is expected to complete the paperwork on the deal at the Blues' training ground tonight.
Winger Gael Kakuta is set to join Benfica on loan as part of the deal for Matic, who has emerged as one of Europe's top midfielders in recent years.
The Serbia international confirmed his departure from Portugal by announcing that last weekend's win over Porto was his final game for the club.
He told A Bola: "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."