With the European transfer window closed and Atletico banned from registering new players until 2018 for breaching Federation Internationale de Football Association rules, Costa will be unable to play for Atletico until January 2.
Costa's departure for a reported £53 million fee means the Blues have made £500m from selling unwanted players since January 2014.
The controversial striker hasn't featured for the Blues this season and doesn't appear to be in manager Antonio Conte's plans going forward. The deal is subject to personal terms and a medical.
Chelsea reach an agreement with Atletico Madrid for the sale of Spain global Diego Costa, subject to personal terms and a medical. In January a training ground bust up with manager Antonio Conte fuelled reports that the Spain global was set for a mega money move to China.
In that time, the Spain global striker made 89 appearances, scored 52 goals, lodged 16 assists and won two Premier League titles and a League Cup.
Atletico said Thursday that Chelsea gave the Spain worldwide permission to travel to Madrid in the coming days to take his medical and finalize the contract with his former club. However, Costa refused to return to Cobham to train with Chelsea.
Indeed, according to Spanish media reports, Costa's return was one of the key demands from Simeone before extending his contract with Atletico to 2020 earlier this month. Although the gap is still vast (Both Manchester United and Manchester City have scored 16 goals, whilst Chelsea have eight goals), this is still a decent record for only five matches played.