Chelsea could use Thibaut Courtois' participation fee in negotiations with Atletico Madrid for Diego Costa.
Should Atletico draw Chelsea in the Champions League semis, they will have to pay a €3 million penalty clause to select on-loan Courtois against his parent club.
The Belgian is desperate to play in the semi-finals, even if it is against the Blues.
And Chelsea could be persuaded if Atletico agree to drop their asking price for Diego Costa. The striker has a £32m buyout clause in his contract.