Mourinho has never hidden his disdain for some of his managerial rivals – with Arsenal's Arsene Wenger and Aston Villa's Paul Lambert crossing swords with the Chelsea boss already this season – and the prospect of a crucial clash with a team capable of ending his side's unbeaten start would usually bring out the antagonist in the Portuguese coach.
However, there should be a refreshing lack of animosity on the sidelines at Old Trafford this weekend, as Mourinho and United manager Van Gaal continue their relation that started 17 years ago at Barcelona.
Mourinho, then working as a translator and assistant to Barcelona manager Bobby Robson, was kept on by Van Gaal when he took over at the Nou Camp and earned the trust of his new boss to such an extent that he was allowed to take training sessions and give team-talks.
Van Gaal saw a kindred spirit in Mourinho and the two men lived only 15 metres from each other in an apartment block, often meeting around their dining tables to talk football.
The partnership lasted until Mourinho left to start his managerial career with Benfica in 2000 but the bond between the pair remains strong, with Mourinho paying tribute to his mentor when asked about van Gaal's influence on him.
"As a young coach to be working with Louis [Van Gaal] at a club like Barcelona was very important," said Mourinho. "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. He knows what I feel about him."
Van Gaal also shared similar sentiments, "He's such a wonderful coach and to see that he's been a champion in different countries is fantastic.”
Despite boasting two of the football’s most enviable CVs, the two have clashed only once before as managers but that was at the grandest of stages; in the 2010 Champions League final, with Mourinho's Inter Milan edging out Van Gaal's Bayern Munich 2-0.
And, while nothing is likely to shake their friendship, Van Gaal would dearly love to avenge that result and show his old pupil that the teacher is still a force to be reckoned with.
Defeating Chelsea would be a significant boost for United, who are 10 points off the top after a stuttering start as Van Gaal continues to overhaul last year’s squad that failed so spectacularly.
Likewise, Mourinho would be relishing the chance to continue Chelsea’s unbeaten run and the Portuguese was quick to highlight that there is more at stake here than their personal relation. "I don't play against Van Gaal. Chelsea plays against Manchester United."
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