Fabio Capello has named Ronaldo as the best player he has coached, but also the worst influence.
Capello coached Ronaldo at Real Madrid in 2006 before sanctioning the sale of the brilliant but troublesome forward to AC Milan.
Speaking at the Globe Soccer Awards, Capello discussed his time at Madrid.
"Ronaldo, the phenomenon, was the greatest player I have ever coached," the Italian coach said.
"He showed up [for pre-season] in Madrid and was 96kg, so I asked him to get to 88-90 kg.
"There was nothing I could do. He was a great player, but a negative influence for the group."
Ronaldo was shown the Madrid door in the January transfer window before Capello's men recovered from a deficit to overtake Barcelona and win La Liga.