"I believe we will win [the title] this season, but I think it will be tougher," he said at the launch of his new book 'Moments.' "Every season I think United, Chelsea, Liverpool and Arsenal will have a chance to win the league. But I think United will win.
"Arsenal and Liverpool look very strong this season. Arsenal are playing fantastic football at the moment. They have a young team, but are doing very well. Liverpool are doing well too, but I believe we are the best team."
Winning the Champions League remains Ronaldo's ultimate dream, but the 22-year-old insists United are more than capable of success both at home and abroad.
"There is always pressure to win trophies every season at this club," he says. "This season is no different. We must win something.
"Winning the league last season meant everything. We had a fantastic season and played a lot of great games. Everyone felt good and fit and I hope everyone will feel the same this season.
"The Premier League and Champions League are the most important trophies and I believe we will win one of them or even both."