Casillas played with Ronaldo for six seasons at the Santiago Bernabeu, winning several titles including the famous ‘La Decima’, before joining FC Porto in July 2015.
Although the former Manchester United and Sporting Lisbon forward scored 28 goals in 43 appearances in his first season in Italy, and helped Juventus secure their eighth consecutive league title, the former Spain international believes Van Dijk and Messi deserves the accolade.
Van Dijk won the UEFA Men's Player of the Year after helping Liverpool win their sixth Champions League trophy.
Messi on the other hand, had a successful year by winning La Liga with Barcelona and many individual awards including the European Golden Boot and FIFA best player of the year award.
According to Casillas, the achievements of the two makes their chances of winning the Golden Ball easier.
"[Virgil] van Dijk was chosen as UEFA's best player; [Lionel] Messi was chosen by FIFA,” the 38-year-old wrote on twitter.
“If Cristiano wins the Ballon d'Or, it would seem to me that the guidelines we use in football to determine who wins its biggest individual awards are not logical.”
Ronaldo and Messi have equally shared 10 Ballon D’ors since 2008, and only Luka Modric broke the monopoly of the duo in 2018.
