The Russian billionaire broke his silence over Mourinho's exit when he bought drinks for a dozen Blues supporters in an extraordinary meeting in the lobby bar of the Spanish city's Hilton Hotel in the early hours of Thursday.
Chelsea owner Abramovich told the fans he will "always love" Mourinho but implied that the arrogant Portuguese manager had started to believe he was bigger than the club.
Abramovich told them: "I love Jose and will always love him because of what he did for Chelsea - but nobody is bigger than the club.
"I understand that you are upset he has gone but things had not been right for some while and the time was right for a change.
"I want you to trust me that Avram is the right man and he is a permanent appointment. There will be more additions to the coaching squad but Avram is here to stay.
"You could see tonight against Valencia we still have a great spirit in our team."
One stunned fan said: "It was a wonderful gesture from Roman to invite us in to the hotel to meet him.
"But some of the fans didn't believe this guy when he said 'Come and have a drink on Roman Abramovich' so they missed out!
"Roman spoke about his love for Jose but clearly wanted us to try to understand the reasons why he had to go. You got the impression, from what he said, that Jose had started regarding himself as a God.
"I don't know if any of us were convinced that Avram Grant is going to be anything other than a stop-gap manager, but I think we left the hotel thinking that at least Roman cares what we think and is still totally committed to the club.
"He speaks better English than he lets on and I don't understand why he doesn't front up in the media."