Portugal out to win first game at Euro 2016.
Ronaldo will be the only captain in the last 16 not to have won a game yet at the tournament
Portugal drew their three group games to claim one of the spots for leading third-place nations.
Ronaldo and co are likely to face a Croatia who will welcome back his Real Madrid teammate Luka Modric and striker Mario Mandzukic from injury.
Croatia coach Ante Cacic pinpointed Ronaldo's ability to turn a game despite Portugal's jaded show so far.
"Ronaldo is their main player, the aim is not to allow them to show how strong he is, we have to limit him," said Cacic.
Portugal coach Fernando Santos bemoaned his side's luck in front of goal in their group games and hopes they get some in the rest of Euro 2016.
"You have to look at these matches, we were better than Iceland, much better than Austria and better than Hungary," he said.
"If we continue to draw and reach the final (on penalties) it is no problem."