Former Real Madrid and Barcelona star Gheorghe Hagi believes motivation is the secret to the success of Ballon d'Or winner Cristiano Ronaldo and his rival Lionel Messi, comparing them to tennis greats Roger Federer and Novak Djokovic.

Ronaldo claimed his fourth Ballon d'Or on Monday to close within one award of Messi, as the two superstars continue their thrilling tussle for the right to be heralded as the greatest player in the world.

Former Manchester United forward Ronaldo won the Champions League and Euro 2016 with Real Madrid and Portugal respectively last season.

And Hagi, an icon of Romanian football who enjoyed his own spell at the game's pinnacle in the 1990s, pinpointed the desire of the two superstars as the driving force behind their sustained levels of excellence. 

"Because he trains, because he heals, always ... he wants to win," Hagi told Omnisport when asked what sets Ronaldo apart. 

"The difference on the field isn't always the motivation in life. [It is] the player's ambition. What you did yesterday no longer works, today you go [onto] the field and you have to be the best. 

"The football players aren't actors. In the movies you make a film and you can watch it 100 times. No, not for the player, each game is different. So you have to be motivated. That's my opinion, the player has to be motivated. 

"This is one of the qualities to become one of the best of the world. One of the qualities of Ronaldo, of Messi, of players that achieve that level is that ... they are motivated."

Having played for both Madrid and Barca, Hagi's loyalties are split when it comes to deciding which star is his favourite, although the 51-year-old did express a fondness for Messi's invention. 

"They are two players that make my life happy," he said.

"We are living [through] a football [era] with two amazing players, one has technical quality and the other has strength. You can have a great body but it all starts in your mind. 

"He [Messi]'s very creative, he has a lot of technique and talent, pure talent. Like in tennis, [Roger] Federer would be Messi and [Novak] Djokovic would be Cristiano Ronaldo."