Cristiano Ronaldo has a solid claim of being the hardest-training athlete in the world, not just in football but across all sports.

The Juventus and Portugal forward’s place among the greatest players of all-time is attributed to his unrelenting determination to be the best more so than his raw talent.

Ronaldo arrived at Manchester United as a skinny teenager with little more to his game than blistering speed and a penchant for unnecessary step-overs.

His potential to become the player he is today was evident shortly after he signed from Sporting Lisbon, though his time at Old Trafford wasn’t without harsh lessons.

According to former Red Devils striker Louis Saha, Ruud van Nistelrooy’s unwavering desire to find the back of the net once led to a disagreement that reduced Ronaldo to tears.

“Ruud had that kind of ego: he wanted all the passes," Saha told FourFourTwo.

“And sometimes, for the development of Cristiano Ronaldo and Wayne Rooney, it was difficult for the manager to deal with.

“Did Ruud make Ronaldo cry? Yeah, there were stories because I think they ended up in an argument at the moment when Cristiano’s father had passed away, so it wasn’t the right moment.

“Things like that happen when two players have lots of spirit, but I’m sure Ruud regrets some of his words.

“Cristiano was just an animal. I don’t know if you can say that he was a human! You could see from when he was 18 or 19 that this guy was not normal.

“These players who have all the ability recognise that it’s also about working harder than anyone - not just talent. The top seeds in tennis don’t hit the ball better or have better technique; no, they work harder than anyone, and Cristiano did that.”

There’s no question Ronaldo was born with a degree of natural resilience about him, though it’s clear that his drive to succeed was fortified on the Carrington training grounds.

The best players on the planet are often shaped by what they learn during the early stages of their careers, and Ronaldo is no exception.