Nemanja Matic will undergo a medical with Chelsea ahead of a proposed £21m return to the club.
The 25-year-old Benfica midfielder arrived in London from Lisbon on Tuesday night.
He is close to completing a move back to the club he left three years ago.
The Serb was valued at less than £5m in January 2011 when he left Stamford Bridge as a makeweight in the deal that saw defender David Luiz join Chelsea from Benfica.
Manager Jose Mourinho quickly identified the defensive midfielder as a key target on his return to Stamford Bridge and the club have no issue with re-signing a player they previously let go.
Chelsea will offset the cost of signing Matic with the £16m they will receive from the sale of Kevin De Bruyne to Wolfsburg.
Matic joined Chelsea from Slovakian club MFK Kosice on a four-year deal for £1.5m in 2009.
He made two substitute appearances in the Premier League and was an unused substitute in Chelsea's 1-0 win over Portsmouth in the FA Cup final in 2010.
Matic joined Vitesse Arnhem on loan for the season in August 2010 before moving to Portugal as part of the Luiz transfer in February 2011.
