The Juventus striker met McGregor at Jennifer Lopez's birthday party in Nobu Villa Atop Nobu Hotel at Caesars Palace, Las Vegas in July 2016.
They liked each other so much Ronaldo turned up at an MMG gym to work out with the Irishman weeks later. McGregor even posted a photograph of them, shirtless and sweaty, on his Instagram account and called Ronaldo an "animal" in the caption.
In an interview with FIFA on Tuesday , McGregor elaborated on what he likes about the soccer player. "Cristiano is a phenomenal athlete, person, and entrepreneur," he said. "His all-around discipline, perfectionist attitude, and dedication to his craft is inspiring and has inspired so many young children to play football."
Juve was 2-0 down in the first leg of its Round of 16 clash against Atletico in February, but with Ronaldo on the team it bounced back last week, won 3-0 on the night and 3-2 on aggregate. Juventus eliminated Atletico because of Ronaldo's heroics, and it is now in the quarter-final against Ajax.
"Just look what he did recently in the Champions League, at 34 years young, a hat-trick under the lights when the pressure was on for all the marbles. And against Atletico Madrid, one of the best defensive sides in Europe.
"That is inspiring! We are both disciplined athletes at the top of our game."
Juventus is not in action until later in the month when it hosts Empoli in a Serie A match on March 30. McGregor, meanwhile, is free to fight from April 6 once he has served a Nevada State Athletic Commission suspension for the role he played in the post-fight brawls that marred his UFC 229 loss to Khabib Nurmagomedov.
It is not yet clear who McGregor will fight in his return to the UFC Octagon.
SEE ALSO: Anthony Joshua has been accused of 'trivializing' rape after saying Cristiano Ronaldo is a hero because he's been 'f-----' by women but is still smiling
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