Russian billionaire Abramovich twice hired Mourinho, in 2004 and 2013, and watched him become the club's greatest manager over his two spells at the helm, notably winning three Premier League titles.
Chelsea's greatest manager...but sacked twice
But he has also sacked him twice, most recently last December, and ahead of the Portuguese's return to Stamford Bridge with United, Mourinho revealed his relationship with his former boss was only ever professional.
"He was never my friend. We had always the relation of owner-manager, a very respectful relation," Mourinho said.
"We were never friends, we were never close to each other. So no, he's just a person that I respected."
Despite Chelsea's dismal title defence last season, which saw them slump to 16th place in the table, Mourinho is likely to receive a warm reception from the Stamford Bridge faithful.
But with United two points below Chelsea and five points off leaders Manchester City in seventh place, Mourinho says he will have more important matters on his mind.
"I'm more focused on the game. I try to prepare myself for the matches, so I cannot say that I care. What can I expect? I don't know," he told reporters after United's 4-1 Europa League win over Fenerbahce on Thursday.
"They (Chelsea fans) can think about me and remember our great relation and have a great reaction.
"They can look at me and say, for 90 minutes he's Man United manager and he's playing against us, so he's not someone that we like in this moment."
"I think I can control my emotion"
But he added: "If you ask me if my team score a goal, am I going to celebrate like a crazy kid? No, I think I can control emotionally that situation."
Mourinho has admitted he will no longer feel a sense of invincibility when he returns to the Bridge.
He avoided a home league defeat in his first three-year stint at Chelsea and prior to a 1-0 Champions League win there with Inter Milan in March 2010 he said the stadium was "lucky" for him.
But having presided over four defeats at the Bridge last season prior to his dismissal, he concedes some of the magic has faded.
"When I played there with Inter, before that I never lost a match at Stamford Bridge because I had that home record that is still in the Guinness (World Records)," Mourinho said.
"Now I lost already a few matches at the Bridge. Last season I lost two or three matches, so I cannot use the same words because now I lost there."
United have already lost to Manchester City and Watford this season and dropped points in draws against Stoke City and Liverpool in their two most recent outings.
But in what could be interpreted as a dig at City manager Pep Guardiola, Mourinho said the leading teams were only succeeding due to the relative easiness of their early season games.
"We are in a period where some teams are having easier fixtures," he said.
"Maybe apparently some teams are going (well), but in a couple of weeks they play between them.
"So my feeling is that it will be really tight. One team that you think is playing for the title in March, probably in May doesn't finish in the top four.
"I'm not a gambler, but if I was I wouldn't bet a lot on the title or the top four because it's a big risk to lose money."