Cristiano Ronaldo's possible obsession with being better than Lionel Messi may have motivated him to join Juventus, according to former Manchester United team-mate Ryan Giggs.

Ronaldo and Messi have battled to be deemed the best player in the world for the past 10 years, winning five Ballons d'Or apiece as Real Madrid and Barcelona fought for supremacy in LaLiga.

The 33-year-old has won league titles in England and Spain, as well as tasting international success with Portugal, something that continues to elude the Argentina captain.

Giggs, who played alongside Ronaldo at United when he lifted the first of his five Champions League titles, believes a desire to conquer Italy may stem from his former team-mate's need to be the best.

"I'm surprised that he would leave Real Madrid and go to Italy," Giggs said on ITV.

"I think it's a big challenge for him but he's going to a huge club. Having that on your CV: Real Madrid, Man United, Juventus - it's some CV.

"He's obsessed with being better than Messi. He has that now, that, 'I did it in England, I did it in Spain, I'm going to do it in Italy ... I did it with Portugal.'

"So maybe that will be his argument when [he asks himself]: 'Am I better than Messi?'"