The 26-year-old was taken to hospital with an apparent stomach bug following the international break with Spain.
The 26-year-old has missed Chelsea's last two games due to reported hamstring and groin problems.
However, it has since emerged that the prolific forward, who is a doubt for this Sunday's Premier League showdown against Manchester United, has been struggling with a virus.
According to BBC Sport, Costa was released from hospital today and his condition is improving.
Costa has scored nine goals following his move to Chelsea from Atletico Madrid in the summer.