Drogba displaces the Brazil international who instead took the number eight jersey vacated by Manchester City loan signing Frank Lampard after the London club released their squad numbers for the new season.
"I am very pleased to be able to return to the number 11 shirt and I am very grateful to Oscar for allowing me to make this change," the influential Ivorian told the club website (www.chelseafc.com).
Drogba last donned the jersey when he scored the winning penalty in the Champions League final against Bayern Munich in May 2012.
He wore the number 15 during pre-season, the shirt he originally had when he first signed for Chelsea from Olympique de Marseille in 2004.
"Didier is a Chelsea legend and a senior player. I am happy for him to take the 11 and for me to take the eight," Oscar said. "Lamps is another legend at this club and I hope I will be as successful in the shirt as he was."
Goalkeeper Thibaut Courtois, returning to Chelsea after a loan spell at Atletico Madrid, has been given the 13 shirt while new signings Cesc Fabregas, Diego Costa and Filipe Luis will wear numbers four, 19 and three respectively.
Manager Jose Mourinho told Chelsea TV he expects Drogba to recover from an ankle injury in time for their opening Premier League game at promoted Burnley on Monday.