Manchester United manager Louis van Gaal admitted he had been surprised by the way his former assistant Jose Mourinho has become one of the world's top managers, saying he could not have predicted it.
Mourinho was on Van Gaal's coaching team during his first spell in charge of Barcelona, between 1997 and 2000, and the two face each other when United host Chelsea on Sunday.
Since becoming a manager in his own right, Mourinho has won the Champions League with both Porto and Inter Milan and seven league titles in four countries.
Van Gaal believes the Portuguese remains a modest man, and stressed that he could not take any of the credit for his success.
"The surprise is that he is now one of the best coaches in the world," he told a news conference. "That, you cannot foresee."
The Dutchman said he believed Mourinho was grateful for his mentors' help and, unlike many in the sport, willing to acknowledge the assistance received.
"He is a very modest and emotional guy," the United manager added. "He is showing [his gratitude], not only for Louis van Gaal but also for Sir Bobby Robson. I appreciate that, but you do it always for yourself.
"I was also an apprentice when I was the assistant coach for Leo Beenhakker [at Ajax]. It is good that my eyes were open at that time, and it is always good that Jose Mourinho's eyes were very open when he was my assistant. But you do it for yourself."
Van Gaal gave Mourinho plenty of responsibility when they worked together at Barcelona, saying: "I know already he has talent because I let him do [manage] some Catalonian Cup matches for me, I let him do that instead of my other assistants. But to see he is such a wonderful coach that he won in different countries, all [as a] champion... I think it is fantastic."
Mourinho famously described himself as "the Special One" and Van Gaal said: "I think every human being is special because every human being has his own identity.
"It is a principle of my philosophy that you have to respect the individual human being. He is very special, but he is very special for me because I have worked with him and we continued a relationship. That, in our football world, is not always normal, so that is nice."
Van Gaal praised the impact made at Stamford Bridge by summer signing Diego Costa, who has hit nine goals in seven Premier League games since arriving from Atletico Madrid but missed the win at Crystal Palace through injury.
It had been thought likely that he would sit out the game at Old Trafford -- but Mourinho has since said he has "a little chance" of playing.
"He scored nine out of seven -- that is remarkable, so he is in a good shape I think, but he was ill yesterday so you never know." he said. "I think he [Mourinho] will play him when he can, because he wants to win."