Messi has broken record after record this season for his goal scoring, and Ronaldo has also had a huge hand in bringing Real Madrid enough success to snatch the La Liga title off Barcelona in the last campaign.
The pair have been heralded for their achievements and are neck and neck to win the Ballon d’Or.
And with Ferguson enjoying a very close relationship with Ronaldo after his time at United, the Scot says the pair can’t be separated for their performances by any critic.
“He (Messi)’s an exceptional young man, there’s no question about that,” he told Yahoo Sport. “The great thing about football is that great players always come up through the decades.
“What we’re seeing at the moment with Messi is an exceptional player in the decade. And Crsitiano Ronaldo another one – both of them, there’s nothing between them, they’re both the greatest players in the world and there’s no question about that.
“You always hope that, even for Manchester United, that you produce a player like we did with Ronaldo.”
Ferguson insisted that any projected rivalry in the media between the two had nothing to do with them excelling in the game, saying: “I don’t think the rivalry bothers them, I think they’ve got their own personal pride in terms of being the best, and I know that because Ronaldo was here (at United) for six .