Rooney could do little yesterday as his side slumped to a 3-0 defeat against Liverpool - which prompted the striker to admit yesterday was one of the worst days of his career.
Despite that Ronaldo believes Rooney, who looks set to become Manchester United's record scorer having put pen to paper on a new long-term contract this season, deserves a place amongst the world's elite.
"I think he's a fantastic player who scored wonderful goals both for the English team and Manchester United," he told rwdfootball.com.
"So I think he’s one of the best strikers in the world."
Both Rooney and Manchester United are enduring a frustrating season under new boss David Moyes following Sir Alex Ferguson's retirement at the end of last season.
They're down in seventh place in the Premier League with their hopes of Champions League qualification all but gone.
They could do with a striker like Ronaldo, who retired from the game as one of the greatest strikers in the modern game and is the all-time leading scorer at the World Cup.
The striker was part of the Brazil team that beat England and their so-called 'Golden Generation' in the 2002 World Cup on their way to winning the tournament.
The Three Lions haven't been beyond the last eight since then, but Ronaldo believes they are still capable of producing world class players.
"I believe there are players here that are already at that high level, players like [Steven] Gerrard in Liverpool, [Wayne] Rooney from Manchester United," he explained. "They are part of that league of high-class players."
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