The two sides clash in Sochi on Saturday evening after finishing first in Group A and second in Group B respectively.
Tabarez, speaking to The Mirror, said that he will take Ronaldo seriously throughout the contest, but added that Fernando Santos's team have other threats.
"[Ronaldo] is one of the best strikers in the world. When he's on top of his game, he's the leader of that team," the 71-year-old said. "There's not one single player who can contain him. Not Diego Godin. Nobody.
"We are going to have to work collectively. We're going to take him seriously but I'm not going to obsess over it. We aren't going to lose any sleep over him. We'll be focused. But nine of those Portuguese players on that pitch are European Champions.
"That speaks of their collective quality. We have a couple of ideas regarding our opponents. Some of my players know them better than I do. I've told them they need to be calm."
The winner of Saturday evening's clash will face either Argentina or France in the quarter-finals.