Atletico remain the only option for Costa, who was told he is no longer needed at Stamford Bridge by Antonio Conte in a text message last month. The arrangement has secured Costa an extra week away from Chelsea but this could be extended.
Chelsea and Atletico have opened talks but have not agreed a fee and Costa is clear that he is willing to accept the terms at his old club, despite their transfer ban preventing them from fielding the Spain international until January 2018.
A rekindling of the relationship between Conte and Costa that helped them on their way to the Premier League title last season seems impossible as Chelsea join up ahead of a pre-season tour of Asia.
Lewis Baker and Andreas Christensen are just two players from the group that spent last season on loan to be watched by Antonio Conte in a training session on Monday. Baker will likely leave on a two-year loan deal to a Premier League club, but Christensen could be used next season.
Antonio Rudiger will be given a holiday after signing for the club in a £34m deal from Roma due to his participation in the later stages of the Confederations Cup.