Goalkeeper Thibaut Courtois is currently on loan at the Spanish side from the west Londoners and he could play a vital role in Jose Mourinho's men securing the services of striker Diego Costa.
Costa has been the shining star from Diego Simeone's attacking style of play as they tussle for the Liga title with giants Real Madrid and Barcelona.
With the long-term futures of all the Chelsea strikers unclear, Costa could bring stability into the starting line-up after a turbulent few months. Fernando Torres, Samuel Eto'o and Demba Ba all seemingly not doing enough to regularly hold down the lone striker role.
Time is running out if Jose Mourinho wants to make this major deal before the transfer window closes, as the January deadline for deals to be completed is Friday evening - little more than two days.
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