The Blues confirmed on their website that Drogba has reclaimed the jersey that he wore during his first stint in London.
Oscar now takes on the No. 8 shirt, which has been vacated by another Blues institution, Frank Lampard.
While Oscar was quoted as saying he was welcome to the shirt: "Didier is a Chelsea legend and a senior player. I am happy for him to take the 11 and for me to take the 8. Lamps is another legend at this club and I hope I will be as successful in the shirt as he was."
Oscar later further explained the move with a post on Instagram: "I couldn't say no to this Chelsea legend that is coming back home. Drogba will wear number 11 this season and I am going to the number 8."
The Blues also offered to refund anyone who'd already had the players' names and squad numbers done for the season and were affected by this late switch.