Leeds United have appointed 'El Loco' as their new head coach - but what have Pep Guardiola, Mauricio Pochettino, Diego Simeone and others said about the Argentine?
Let's take a look...
Pep Guardiola (Manchester City manager)
"My admiration for Marcelo Bielsa is huge because he makes the players much, much better. Still, I didn't meet one guy, a former player from Marcelo Biesla who speaks no good about him.
"They are grateful about his influence on their careers in football.
"He helped me a lot with his advice. Whenever I speak with him I always feel like he wants to help me."
"It is important for me to say this about Marcelo because it doesn't matter how many titles he had in his career. 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. That is why, for me, he is the best coach in the world."
Mauricio Pochettino (Tottenham Hotspur manager)
"He is like my football father. We are a generation of coaches who were his disciples.
"How he feels football, the passion he has for football, I think we all took that from him."
Diego Simeone (Atletico Madrid manager)
"I have the influence of several coaches: Bielsa, [Sven-Goran] Eriksson, [Alfio] Basile ... they have left a mark."
"Bielsa taught me the most."
Anwar El Ghazi (Lille player)
"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."
Benjamin Mendy (Manchester City player)
"He made me devour videos like never before.
"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."