Barcelona great Xavi softened his attitude towards Louis van Gaal during the coach's Camp Nou tenure, having initially worried the Dutchman was an "idiot".
Van Gaal handed Xavi his Barcelona debut against Real Mallorca in the 1998 Spanish Super Cup, the midfield maestro marking the occasion by scoring in a 2-1 defeat.
After departing to coach the Netherlands national team in 2000, Van Gaal returned for a second spell in Catalonia two years later - by which point Xavi was a long-established fan of his work.
"He's honest, methodical and a real perfectionist," the 35-year-old said in an interview with ESPN.
"He's very demanding, he's strict and he wants to achieve the highest levels possible.
"After two days of training under him, I thought, 'Who is this idiot?' After a week, I thought, 'He's right.'
"He'll always be in my heart, Louis van Gaal."
Van Gaal is yet to win such strong affection from many Manchester United supporters, with his style of play at Old Trafford coming in for regular criticism over perceptions of it being too defensive.
Xavi believes his old boss is "poorly valued by the media" and suggests he has mellowed with age.
"He has a very strong character, but he's calm in the Premier League because there's less pressure.
"He's much calmer than when he was at Barca or Bayern Munich."
Xavi also had first-hand experience working with Jose Mourinho at Barcelona.
The Chelsea manager stayed on as Van Gaal's assistant after working under Bobby Robson at the Camp Nou.
Mourinho was initially employed as a translator to the veteran English coach and the former Real Madrid boss is often derisorily labelled as such by Barcelona fans, with whom he is now deeply unpopular.
"Rubbish," said Xavi before explaining that Mourinho was far more than a go-between for players and staff.
"He was the assistant coach, someone who understood the philosophy of Barca and who shared many of the same characteristics of Van Gaal.
"He was very respected by the players. He trained us sometimes alone at Barca B and he was excellent.
"I'm surprised that he became known for another type of football, more defensive, because he wasn't like that with us."