Downbeat: Real Madrid's Cristiano Ronaldo (Picture: REUTERS)

Cristiano Ronaldo's 'unhappiness' at Real Madrid has been revealed as a row over the players image rights, according to reports in Spain.

Ronaldo shocked world football earlier this month by revealing that he was considering his future at the Santiago Bernabeu, after a behind-the-scenes row left him 'sad' with his position at the club.

The Portuguese superstar refused to clarify what the issue is, but he denied a fortnight ago that his disappointment with Madrid was a brazen attempt to earn a bumper pay rise as part of a new contract.

However, according to reports in Spain this week, the ongoing row between Ronaldo and Real IS down to money - the amount the club earn from his lucrative sponsorship deals, to be exact.

Ronaldo agreed to a 60:40 split of all money earned from sponsors when he signed for Madrid in a world-record £80 million deal in 2009, but despite already getting the larger percentage, he has allegedly demanded that he is paid 100% of all money from now on.

The issue is dominating negotiations over a new contract, and Ronaldo is said to have been left furious by president Florentino Perez's refusal to even entertain the idea.

It is understandable though, given the 27-year-old reportedly picks up close to £20 million per year in various endorsements ranging from sports brand Nike to video game Pro Evolution Soccer.

Ronaldo has three years left to run on his current contract.