The Spain striker had a bust-up with Blues boss Antonio Conte in January and was the subject of a bid from the Chinese Super League.
The pair resolved their issues but doubts remain about the 28-year-old’s long term future at Stamford Bridge.
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Atletico Madrid attempted to sign Costa last summer and would target him again if he became available.
And Wilkins, a former coach at Chelsea, feels Conte will be considering possible replacements if Costa leaves.
Could Diego Costa leave Chelsea in the summer?
"They'll be delighted to be in that Champions League, they would have missed it immensely this season," Wilkins told Sky Sports.
"It really depends on Diego Costa, to a large degree, who they are going to get in to replace him if he decides to go to China, which has already been mooted this season.
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Chelsea striker Diego Costa
"It will be very interesting, I'm sure Antonio will have a few names up his sleeve that he would like to bring in. Defensively they have spoken about bringing added players in.
"But at this moment in time they just need a few additions to keep themselves bubbling along – they are all young enough and they all look absolutely superb at the moment."