Carlo Ancelotti says Cristiano Ronaldo has taken professionalism to another level, including taking ice baths at 3am.
Ronaldo worked under Ancelotti for two seasons at Real Madrid, with the pair winning the club's historic 10th Champions League together in 2014.
Ancelotti has also coached some of the world's best players at AC Milan, Juventus, Chelsea and Paris St-Germain.
But he says Ronaldo stands out as the most professional player he has ever worked with.
"Truly, the most. I watched the film (Ronaldo's documentary) and it was good but it did not show how professional he is," Ancelotti told the Daily Mail.
"We would sometimes return from a European game. It could be three in the morning but Ronaldo would be the player who did not go straight home. Instead, he would go to the training ground for the ice bath, to help with his recovery from the game."
It has been reported that Ronaldo had a cryotherapy chamber installed at his house in 2013 to aid recovery while Ancelotti's previous assistant Paul Clement told The Guardian he got a sports massage from a physio at 6am after a trip back from Istanbul.
Ancelotti has been out of work since being sacked by Madrid in the summer, although there has been speculation that he could return to Chelsea.
He was dismissed by Madrid a year after winning the Champions League and said it was the hardest job he has done.
"Was losing to Liverpool in 2005 [with AC Milan] my worst experience? Try losing 4-0 in the Madrid derby," he said. "That season, we had a run of 22 wins in succession but it was all forgotten on February 7 when we lost 4-0 to Atletico.
"'If the manager doesn't win at Madrid, he is sacked. Had I not won the Decima, I would have been sacked a year earlier but I knew this when I took the job. I could have decided not to sign, but Real Madrid is the most important club in the world."