The Portuguese won the Premier League in 2005 and 2006 with the London club, who have put Russia coach Guus Hiddink in charge until the end of the season after sacking Luiz Felipe Scolari on Monday.
"If you ask me if one day I think I will return to Chelsea, I will tell you yes I think so, I think so because we were so happy together," Mourinho told a news conference ahead of Sunday's derby against AC Milan.
"But when I say one day, I am not saying to you when."
Mourinho left Chelsea in September 2007 but said he was still a fan of the club.
SPECIAL FRIENDS
"I am not there, I am just a supporter from the outside," he said. "I'm somebody who wishes them good because it's a special club for me, I have special friends there.
"I belong to their story, they belong to my story so I am not enjoying this period where they have had several managers in one year and a few months.
"I hope they find stability and go back to (winning) trophies."
Mourinho was succeeded by Avram Grant, who was then sacked in May 2008.
The Inter coach, whose team have a seven-point lead at the top of Serie A, said he was not surprised to see England midfielder David Beckham doing well during his loan spell at AC Milan from Los Angeles Galaxy.
"I knew in advance all the fears people had about him were not fair," said Mourinho. "I knew he was a top professional, he arrived in great condition with great ambition.
"He has adapted very well, he is playing very well. He is giving different kinds of qualities to his team and I hope he stays for the good of the league."
