Denmark, surprise joint leaders of Group B, won their qualifying section ahead of Portugal, largely due to a 2-1 home victory over them.
"We have closed down Cristiano Ronaldo before and we firmly believe we can do it again," said defender Simon Kjaer, one of the Danes' best performers in a surprise 1-0 win over Netherlands in their opening game at the finals.
"He has got unique individual skills but we have shown before that we can cope with him as a team and we believe that we can defeat Portugal again," Kjaer told reporters.
Although Kjaer bullishly said the Danes had "blown the group right open", coach Morten Olsen sounded more cautious in the wake of the 1-0 win over an unusually wasteful Dutch side.
"A bit of euphoria is great but we will keep both feet on the ground. We have to do better against Portugal because they are under a lot of pressure now," he said.
"We will try to continue on our path and play well. Let's work to be a little more efficient and look for the luck we've been missing in recent games," said coach Paolo Bento.
Helder Postiga made little impact against Germany as the lone striker in Portugal's 4-3-3 formation and must be under threat from young striker Nelson Oliveira, who Bento has tipped as a player for the future.
