Barcelona forward Messi helped his side win La Liga with his stunning goal haul last season. Ronaldo is the current favorite having shone bright for Real Madrid but lacks any silverware, while winger Ribery starred as Bayern Munich romped to treble success in 2012-13.
Three-time Ballon d'Or winner Platini is in no doubt as to the favorites for the FIFA accolade, who he is unable to separate, and joked that the deadline extension for votes could have been for Ronaldo's sake after his public spat with Sepp Blatter.
"It seems that the favorites are Messi, Cristiano Ronaldo and Ribery," he mused to AS. "The first two are very good and Ribery is the one who has won everything. They are three great players. The choice of the Ballon d'Or this year is the most difficult in the history of the trophy.
"The voting extension was a FIFA decision, though it happened to coincide with Portugal reaching the World Cup thanks to three goals from Ronaldo against Sweden.
He added, laughing: "It may be that FIFA has done it to please Cristiano..."
Platini also rued the fact that a Spanish player did not win the award after the nation won the 2010 World Cup, with Messi instead taking home the second of his current four Ballon d'Or titles.
"I do wonder about why [a Spain player didn't win]," the Frenchman added. "I agree that, in 2010, the Ballon d'Or winner should have been Spanish.
"Andres Iniesta, Xavi... For me, one of them deserved it. Messi won it and he is a great champion. But in 2010, for me, it had to be a player from Spain that lifted the trophy."
The Ballon d'Or award ceremony takes place on Jan. 13, with voting having closed on Nov. 29 after a two-week extension from the original date.