The Ivory Coast striker departed Stamford Bridge in the summer of 2012 after guiding the Blues to Champions League glory and now finds himself with Turkish club Galatasaray.
On Tuesday night, Drogba and the Istanbul outfit meet Chelsea in the Round of 16 second leg of Europe's premier club competition - marking his firs return to the club since he departed - but Mourinho does not believe it will be the last.
"That's not for me [to decide]. That's for Chelsea [to decide]. I think it has to happen one day," he told reporters.
"When? I don't know. As a player, as a coach, as an ambassador? Next year, in four to five years, in 10 years? I don't know. But when a person represents so much to a club and when a club represents so much to a person I think he has to be welcomed back.
"Undoubtedly he's one of the most important players of the history of this club. That's not a doubt.
"All Chelsea supporters agree with that. We don't say the most important one because that's not fair for other people that was in the same level and in the same generation.
"Is he the same player at 36 than he was at 26? I think nobody is but he is one of the best strikers in the world. That's for sure."
Drogba, who first joined Chelsea from Marseille in 2004, added fuel to the Mourinho fire by suggesting that he could be interested in perhaps heading back to the Bridge in some capacity after he ends his playing career.
"I can't turn my back and say I will do something different, maybe as a coach maybe something different," he said.
" will stay in football. Do you want to work here (Chelsea)? Yes of course but not now I still want to play."
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