Mourinho was the Dutchman’s assistant at Barcelona when Van Gaal was manager at the Nou Camp in the 1990s, before going on to become one of the most successful managers ever. On Sunday the pair meet for just the second time in the opposite dugouts with Mourinho winning the only other game; the 2010 Champions League final between Inter Milan and Bayern Munich.
"I don't play against Louis," Mourinho said in a pre-match press conference.
"Chelsea plays against Man United. As a young coach to be working four consecutive years - one with Mr (Bobby) Robson, three with Louis - at a club like Barcelona was very important.
"It's not the moment for that. Everybody knows the respect I have for him. I never hide the respect, the relationship and the fact he was an important influence in my career.
"But, please, he's going to be my opponent, so don't make me speak for half an hour good about him.
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"He knows what I feel about him. The world knows, because I never hide. What can I add? I have nothing to add."
The Portuguese manager also declined to analyse United’s season so far, as he attempts to continue Chelsea’s league-leading form.
Last season Chelsea managed a 0-0 draw at Old Trafford, playing Andre Schurrle in a ‘false 9’ position; Mourinho may be forced to do something similar on Sunday with Loic Remy missing and Diego Costa having “a little chance” of playing, according to the manager.
"We go to every match to win," Mourinho added.
"Sometimes matches go in one direction where in a pragmatic way you feel that one point becomes a good result.
"Sunday we go to win. If you give me now one point and I don't go and I don't play, I don't accept the point you give me. I want to fight for the three points."
Mourinho believes United remain a difficult opponent despite the recent travails.
He said: "For me it doesn't matter the manager, the moment, the table, the players - Man United is Man United and I always look at them independent of these factors.
"I like to play big matches, I like to play against the best teams. I like to play in the most difficult stadiums.
"I know the risk of not getting a good result is bigger in big matches. But I always like.
"For me to go to Old Trafford - I did it with four different clubs, with Porto, with Inter, with Real Madrid and with Chelsea - I like to go there, I like to play there."
Additional reporting from PA