The Portugal skipper spearheaded his club side, Real Madrid's, charge to the Liga title with a multitude of goals last season, leading many to speculate as to whether he is the world's finest footballer at the moment.
However, Rosicky feels that the 27-year-old must help out his defensive colleagues more often to be considered an equal to the best players in the game.
"He’s a good attacker, but he doesn't want to defend," Rosicky said according to The Sun.
"Sometimes you can be so good you can afford not to help the defence and just score goals. But is he the best player in the world? I don't know if he is worthy."
|Portugal v Czech Republic
Despite the Czechs being underdogs to progress further in the competition, the former Borussia Dortmund playmaker feels that the gulf in quality between the two teams is not as wide as people suggest.
"People say Portugal are the favourites, but how do you recognise a big team? Especially out here, all the teams are strong and only small details will decide who wins," he continued.
"There are not five big teams then the rest of us. This will be one of our most difficult matches in the Euros but we feel we have a chance to go through even against Portugal."
However, Czech Republic boss Michal Bilek has different views to the those of his captain after watching Ronaldo see off Netherlands to secure Portugal’s place in the quarter finals.
The 47-year-old has warned his side that it will take an ‘exceptional effort’ to keep out the Portuguese captain.
"Ronaldo is an excellent player and we will adjust our tactics to reflect that, be more defensive. He can score 40 or 50 goals a season, to defend against him takes an exceptional effort," he said.
"We must not give him any space or it is impossible to stop him. We don't have stars, beyond perhaps Petr Cech and Rosicky, if we defeat Portugal it will be down to the team.
"Russia punished us for opening up too much but we strengthened the defence and that was the key."