"If Cristiano doesn't win the Ballon d'Or this year, it's only because he's not nice, because he doesn't sell his image well," Mourinho was quoted as saying in Friday's Portuguese sports daily A Bola.
Unlike Messi, Mourinho added, Ronaldo had won a major title with Real - the Spanish league.
But the Barca and Argentina forward has nevertheless won the last three Ballon d'Or, the prestigious award for the world's outstanding footballer.
"Messi has grown up in the team in which he plays, with the players he plays alongside. Not Cristiano, who was in England and whom we put into a team that was a losing one," the Portuguese coach said.
Ronaldo is 'a winger who scores as many goals as a No 9, a player who is not protected from anything or anybody'.
"It's much tougher being Cristiano than Messi," insisted Mourinho.