Cristiano Ronaldo has an irregular extra bone in his ankle - a condition that only affects 10 per cent of the population.
The discovery was made when the Real Madrid striker, who has been talismanic for the Champions League holders, received treatment on an injury five years ago.
Ronaldo went to doctors after suffering a knock while playing for Real against Marseille in 2009, as revealed in a new book CR7 - The Secrets of the Machine, written by Luis Miguel Pereira and serialised in the Sun.
A course of physio sorted the extra bone out without the need of an operation.
Fitness has always been a fascination for Ronaldo, who was caught using Sporting Lisbon's gym late out of night without permission.
A security report stated at the time: 'We hereby wish to inform you the athletes Cristiano Ronaldo and Jose Semedo used, without permission, the main fitness and bodybuilding gym where they were found at 11.30pm by the security guard.'
Youth coach Luis Martins said: 'I explained to Cristiano that he couldn't go further than what was prescribed to him because that would be harmful for his body and health.'
The news hardly comes as a surprise, given the 29-year-old has always been slightly different to the norm.
Ronaldo carried Carlo Ancelotti's side for large parts of last season and prised the Ballon d'Or off Barcelona's Lionel Messi.
The former Manchester United man scored more goals than anyone else has done before in Europe and sealed the trophy in Lisbon on Saturday night against city rivals Atletico