Having moved into a false nine position, Messi went up another level under the Catalan, winning three La Liga titles and two Champions Leagues in a stunning four-year spell.
He netted 211 goals in 219 games playing for Guardiola and also collected three Ballon d'Or wins before scooping a fourth a few months after he left for a sabbatical.
And Guardiola introduced a few interesting techniques in order to get the absolute maximum out of Messi's supreme talents.
According to Samir Nasri, who briefly played under Guardiola at City, Messi had an intercouse curfew - brought in order to improve his muscle recovery.
“For him, his players’ sexual activity must take place before midnight in order to get a good night sleep – even if they are free tomorrow," Nasri told L'Equipe du Soir, via the Daily Star.
“He [Guardiola] said that he placed this rule on Messi and his muscles improved since.
“He told us this is how he managed to get the best out of [Robert] Lewandowski too and for them to avoid the maximum number of muscular injuries.
“He suppressed many things that were in the kitchen.
“He will not bully you, but he will do everything to make you progress, to get you to know you how to position yourself and how to play. He’s a picky person.”
Nasri's stint playing for Guardiola was very brief. The former Bayern Munich boss arrived in the summer of 2016, when Nasri had just returned from an injury.
He only made one appearance in that first season, a late cameo in a 3-1 win against West Ham, before being loaned out to Sevilla.
Despite admiring his abilities, Guardiola was not happy with Nasri's condition.
He explained: “Guardiola told me that I was a mess, he told me several times and even kicked me in the butt, literally.
“When I returned from holiday having had a year with injury problems and personal life problems, I was a little out of shape.
"Not as much as what was said but a few, four kilos overweight; For Guardiola, over 2.5 kilos and you do not you train with the group.
“Guardiola told me with your qualities you should not be at Manchester City, you should be at Barcelona. We had some discussions, he wanted me to stay and play for him. I told him no, because he couldn’t assure me a first team place.”
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