Nemanja Matić's return to Chelsea is close to completion after the club confirmed he will undergo a medical ahead of his £21 million transfer.
Matić, who left the Blues for Benfica in 2011 as part of the David Luíz deal, will become the club's first signing of the January transfer window.
The 25-year-old Serbia international was sold by Carlo Ancelotti three years ago but has impressed in Portugal, and faced his former club in last year's Europa League final.
Despite reporting a £49.4m financial loss for the year to 30 June 2013, Chelsea will offset the Matić deal by selling Kevin de Bruyne to Wolfsburg for a fee of around £18m.
The arrival of Matić will quell Chelsea coach José Mourinho's concerns about the state of their midfield, where there is insufficient protection for the back four.
Although John Obi Mikel has been tasked with shielding the defence, Matić is a livelier option and will help fill the void when Frank Lampard leaves the club.
Lampard, 35, is out of contract in the summer although he has reportedly been offered an extension.