The winger admits there is pressure on his side.
With four games remaining Portugal must beat the Danes and hope the leaders drop more points in their remaining fixtures, otherwise the best they can hope for is a play-off place.
Group leaders Denmark are so far undefeated and produced a stunning late show last September, scoring two stoppage-time goals, to beat Portugal 3-2 in Lisbon.
Portugal have four games remaining, starting in Copenhagen on Saturday, followed by a trip to second placed Hungary before hosting Hungary and Malta in October.
"There is great pressure, that is true. It's normal, with everything at stake but I am sure we will achieve victory and my team will be at the World Cup in South Africa," Ronaldo told AS.
"I am convinced Portugal will be at the World Cup. For sure."
Paul Madden, Goal.com
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