The 28-year-old Brazil-born Spanish international is still keen on a return to Atletico despite them not being allowed to field new players until January because of a transfer ban.
“Another absentee (new signing Antonio Rudiger was also absent) was Diego Costa, after it was agreed with the club that he should have an extra few days off,” read a statement on the club website.
Costa enjoyed a fractious relationship with Chelsea manager Antonio Conte last season despite scoring 20 goals in 35 league appearances in Chelsea’s title-winning campaign.
Indeed the player revealed last month the Italian had texted him to say he was no longer part of his plans.
However, Conte’s aim of replacing Costa with Romelu Lukaku went badly astray when the Belgian international jilted Chelsea’s advances for Manchester United’s, despite both clubs offering the same transfer fee of £75million ($97m, 85.5m euros).
Costa — whse contract runs till 2019 — caught the eye in his four-year spell at Atletico before joining Chelsea for £32million in 2014.
Last month Atletico lost an appeal against a FIFA-imposed sanction which means that, while they can still buy players this summer, they will not be able to register or play them until January.
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