Chelsea are on the brink of re-signing Nemanja Matic from Benfica in a deal worth £20.7million, Goal understands.
Talks will be held in Lisbon on Monday in an attempt to finalise the Serbia international's transfer back to London.
Chelsea are believed to have made a bid of £18m rising to £20.7m in add-ons for Matic, 25.
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It represents a huge mark-up for the west Londoners but manager Jose Mourinho regards Matic as the type of midfield anchorman the team has been lacking for several years.
Tall, athletic and comfortable with the ball at his feet, the Serbian will be expected to slot straight into Mourinho's side if the deal can be completed in the coming days.
Chelsea are said to be confident of agreeing the details with Benfica and imminently announcing Matic as their marquee signing of the January window.
The Europa League champions expect to partly finance the transfer by using the funds from Kevin de Bruyne's imminent sale to Wolfsburg, with the Belgian on the verge of a £15m move to the Bundesliga.
Mourinho has been keen to buy a proven defensive midfielder since returning to Stamford Bridge last summer and finding a squad overloaded with playmakers and light in the central areas.
With defender Luiz regarded as a last resort in midfield, Frank Lampard out of contract in the summer and Marco van Ginkel sidelined for the season with a cruciate ligament injury, strengthening in that area has been regarded by the Blues as a priority.