Pep Guardiola and Mauricio Pochettino will be big rivals in the Premier League this season, but they have one thing in common; they both call Marcelo Bielsa the "best coach in the world".
This is the era of the "super manager" in the English top flight: Jose Mourinho, Jurgen Klopp, Arsene Wenger, Antonio Conte, Pochettino and Guardiola.
And although Bielsa's trophy cabinet might be on the light side, arguably none of them can claim to be more influential in football than the 62-year-old former Chile and Argentina boss, who is now head coach of Lille in France.
Guardiola's mentor and Pochettino's "father"
"My admiration for Marcelo Bielsa is huge," Guardiola says.
The Manchester City manager travelled to Argentina in 2006 to seek out his advice about becoming a coach and the two have been close ever since.
"He makes the players much, much better and he helped me a lot with his advice."
"I am pretty sure his influence at Lille - their club and their players - will be huge. Amazing. I am pretty sure of that."
Spurs boss Pochettino was born in the Argentine village of Murphy, north of the capital Buenos Aires. He first came into Bielsa's orbit when he was 14.
"He is like my football father," says the 45-year-old.
"We are a generation of coaches who were his disciples," he told SFR Sport. "How he feels football, the passion he has for football, I think we all took that from him."
Jorge Sampaoli [Argentina boss], Diego Simeone [Atletico Madrid manager], Gerardo Martino [Atlanta United boss] and Sevilla head coach Eduardo Berizzo all cite Bielsa as a major influence on their style of management.
At the age of 18, central defender Pochettino won the Argentine title with Bielsa's Newell's Old Boys in 1991 and reached the final of the Copa Libertadores the following season, losing to Sao Paulo on penalties. It was a stunning achievement for a modest club.
Bielsa tasked the players at the club with scouting the opposition and asked them to present their reports in front of the squad. In an age before the internet, he told them to read three newspaper reports of their previous game, as well as sports weekly El Grafico.
Mysterious and unpredictable
Bielsa is seen by many fans and journalists as a mysterious figure because he never gives interviews, only pre and post-match news conferences.
He is also unpredictable.
Lack of trophies
But can he really be considered as one of the best coaches in the world when his trophy collection is relatively small?
Three league titles in his native Argentina and an Olympic gold medal in 2004 with the national team don't compare to the greats of the game.
And there are a number of disappointments in finals.
Guardiola though, feels that's irrelevant: "We are judged by that - how much success we have, how many titles we have won but that is much less influential than how he has influenced football and his football players."
"Still, I didn't meet one guy, a former player who speaks no good about him. They are grateful about his influence on their careers in football."
'Just a bedroom, air conditioning and electricity'
So what makes Guardiola and Pochettino rave about Bielsa? And what is he really like to play for and work with? World Football has been to Lille to find out more about the manager nicknamed "el loco" [the crazy one]."
Pre-season has been very different for the Lille players this year. Not only did they work at the training ground but they also lived there.
Bielsa asked for about 20 "bungalows" to be built at their Domaine de Luchin headquarters.
"We started pre-season on 19 June," says Lille winger Anwar El Ghazi. "The first two days were tests and after that it was hardcore. We trained at 10am and second training was 6:30pm. We eat here, we sleep here and we do everything here.
"They're small bungalows, just a bedroom, air conditioning and electricity, that's all. If you want to take a shower you go to the changing room and we have a room with Playstation and table tennis.
"The coach said we had to be a family together and when you're eating together, sleeping next door to each other, you become a family. We are like brothers now."
Extreme (el loco) intensity on and off the pitch
Bielsa was attracted to Lille by the vision of two men, the owner Gerard Lopez [ex-president of the Lotus F1 team] and the former vice president of Barcelona Marc Ingla, who is now director general of Lille.
Ingla played a big part in the appointment of Guardiola as head coach at Barcelona in 2008 and working with Bielsa is bringing back memories.
"He reminds me of Pep Guardiola sometimes in the way that he has an extreme intensity," said Ingla.
"Playing at extremes always generates stress in the systems but I think it's good to push everybody and every single point or lever that can make us better. The players, the club or the infrastructure at the training ground."
El Ghazi said: "He is a little bit different, he can be very aggressive and shout at people but then he'll be very quiet.
"He pushes everybody to the limit, for example my body fat used to be 10% or 11% and now it's 8%.
"We train a lot, it's very physically and mentally hard.
"You do the kind of actions that you do on the pitch. We train like a realistic game, like passes you would do during matches, those type of things. Training is very different to what I experienced when I was playing at Ajax. We don't do position games and we don't do a lot of matches during the training sessions."
Research, research and more research
Bielsa is famous for his obsessive use of videos to prepare for matches and it's something he has already brought to Lille.
Man City's new left-back Benjamin Mendy - who played under him at Marseille - sums this up best.
"He made me devour videos like never before," Mendy told Onze Mondial.
"To begin with he put me in front of the videos and I'd fall asleep. But he was happy! I was shocked.
"After a while I stopped sleeping and told myself 'go on, I'll watch two minutes of this thing after all.'
"After that he talked to me, I talked to him and we'd go over moves together. He told me, 'see, that's why I let you sleep. You slept, you slept, you slept but the day you decided to watch you got interested on your own. If I'd pushed you to watch you wouldn't have been interested'... Marcelo is just too good."
When he arrived at Athletic Bilbao it is said he watched all of their matches from the previous season, making reams of notes on every single game.
And after joining Marseille there were even reports that he watched all of their games from the previous season up to 13 times.
Bielsa's Chile teams caught the eye with their 3-3-1-3 formation and attacking football, pressing high up the pitch.
In March 2012, Manchester United fans applauded Bielsa's Athletic Bilbao off the pitch after a stunning performance in the first leg of a Europa League last-16 tie.
"With Marcelo in charge we shouldn't be shy in saying we want to put together the greatest football, with the greatest coach for what we're trying to do," Ingla says.
"That's a spectacular, offensive, winning style and we believe he can be the greatest executor of our plan."
"We want to excite the crowd and surprise the crowd with spectacular pressing football."
Spotting young talent and giving youth a chance
The average age of Lille's first XI in their first game of the season was just over 23. The oldest player on the pitch was only 26.
Bielsa has cast aside older, experienced players such as Vincent Enyeama and Rio Mavuba to give younger players an opportunity. It's something that's had a big influence on Pochettino's philosophy.
"We went for Marcelo because he is the best coach to develop young talents to their maximum potential," added Ingla.
"It was a natural fit for our vision. He can be the greatest executor of our plan."
In 2014 at Marseille, he said this about a 19-year-old Mendy: "You may think I'm joking, but Mendy will be one of the best full-backs in the world."
Mendy cost Man City £52m.
Meanwhile Pochettino says Bielsa spotted that he had the potential to be a top footballer when he was fast asleep.
He'd arrived at the family home at 2am and asked the Spurs boss' parents if he could see their teenage son's legs. Bielsa then announced he was signing him for Newell's because he looked like a footballer.
"Yes, that was the reality," Pochettino told Sport Magazine. "I woke up in the morning and my mum explained the story. I said: 'Yeah come on, it was in your dream. What did you drink before you went to sleep?'"