The pair have maintained a close relationship since former Barcelona boss Van Gaal gave the self-styled 'Special One' some early coaching opportunities as the Portuguese worked under him for three years at the Nou Camp.
The Dutchman says he is not surprised at Mourinho's emergence as one of the world's best managers and feels privileged to have played a part in his development.
"I knew already he had talent because I let him do Catalunya Cup matches for me instead of my other assistants," Van Gaal told a news conference on Friday ahead of the visit of the Premier League leaders.
"But to see that he's such a wonderful coach and won in different countries, all championships, I think it's fantastic,” he added.
"He has said (he learned from me) and it's remarkable because in the football world not many people are talking about that. He says it is not only about Louis van Gaal but also (former Barca manager) Bobby Robson. I appreciate that but you always do it by yourself,” the Dutchman said.
"He is very special for me because I've worked with him and we've continued our relationship which in the football world is not always normal," added the former Bayern Munich coach.

"He is a very modest and emotional human being and I like that,” he said.
The pair have only clashed once before in a competitive game when Mourinho's Inter Milan beat Van Gaal's Bayern Munich 2-0 in the 2010 Champions League final.
Hosting his former assistant on Sunday will be another difficult task for the United boss with Chelsea in devastating form, dropping only two points from their opening eight games to open up a five-point gap on nearest rivals Manchester City.
In contrast Van Gaal has endured a stuttering league start since taking over in the close season, with his side in sixth place in the table and 10 points adrift of Mourinho's men.
"Jose has worked more than one year already with his team and last year they didn't win any prizes so you have to build up and he has built up Chelsea," said the Dutchman.
"They are playing like a team and I want my team to do that as well but to play for 90 minutes," he added.
United have been handed a boost with British transfer record signing Angel Di Maria deemed fit to face Chelsea.
The Argentina winger limped off when his team snatched a 2-2 draw at West Bromwich Albion on Monday but Van Gaal said he had trained ahead of Sunday's match.  

Costa may return against United, says Mourinho

Meanwhile,  Diego Costa, Ramires and John Mikel Obi could all return to the Chelsea squad for their Premier League clash with Manchester United at Old Trafford on Sunday, manager Jose Mourinho said.
But striker Loic Remy is definitely out.                

The three all missed Chelsea's 6-0 Champions League club record win over Maribor on Tuesday, but Mourinho said they all have "a little chance" of playing against United, and he would decide after Saturday's training session.
Costa, joint top scorer in the Premier League with nine goals, has missed the last two matches with a hamstring injury and then a virus, while Ramires has missed their last six games with a groin injury and Mikel the last two with a bad foot.
Remy, though, will be out for two to three weeks after injuring his groin scoring the opening goal of the win over Maribor at Stamford Bridge.
Asked if he had any positive news about Chelsea, unbeaten in 12 matches in all competitions this season, Mourinho bounced back: "I only have positive news.
"We are playing well, we are confident, we are top of the league, we are in a good position to qualify for the Champions League, the camp is happy and we are ready for the game,” he added.

 Although United are down in sixth place with only three league wins from eight so far, Mourinho says going to Old Trafford is always special -- and that his friendship with Van Gaal will be put on hold for 90 minutes.
"It doesn't matter who the manager is, or the moment, or the league table, or the players, Man Utd is Man Utd and I always look at them through these factors,” he said.
"But tomorrow I don't play against Louis, Chelsea plays against Man Utd and during the match I have no time, and he has no time to look around and to see who the opposing manager is,” he added.
"Before the match and after the match he is one of my big friends in football so I am always happy to see him.
"Everyone knows the respect I have for him but please on Sunday he is my opponent so don't ask me to speak about him for half an hour now,” he further said.

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