The monstrous Polish centre back pairing of Michal Pazdan and Kamil Glik face their toughest challenge yet when they come up against Portugal in the last-eight clash in Marseille on Thursday, though their previous matches have not provided much by way of preparation for facing the Real Madrid star.
Describing 29-year-old Ronaldo as the "perfect athlete", U.S. lifestyle magazine Men's Health says he hits speeds of more than 32 kph, jumps nearly a metre in the air off one leg, runs an average of 16 km per match and hits more winners in the last 20 minutes than anyone else.
He is the only player to have scored a goal in four Euros going back to 2004 and, while he struggled to find his feet early in this year's tournament, there are signs that he is back to his sublime best.
He scored twice in Portugal's last group match against Hungary -- an audacious back heel and a towering header -- and has had a hand in two of his country's other three goals, most importantly the shot that set up Ricardo Quaresma to score the easiest of extra-time winners in their last-16 win over Croatia.
For their part, Poland are good shotstoppers.
They have conceded just three goals all year and only one in the Euros, an outrageous bicycle kick by Switzerland's Xherdan Shaqiri in their round-of-16 tie which they eventually won on penalties. Only Germany still have a clean sheet in Euro 2016.
Poland's matches in France so far will have done little to prepare them for the pace, power and superhuman heading ability that Ronaldo possesses, however.
Their top-ranked opponents to date, Germany, fielded the diminutive Mario Goetze in their group-stage stalemate and the 'false nine' presented little trouble in the box, constantly dropping back into midfield to pick up the ball.
Other group matches against Northern Ireland, who did not get a decent effort on target, and Ukraine, who departed after failing to score in any of their games, were fairly straightforward.
The late Shaqiri wonder goal in their last outing did unsettle the Poles, with Switzerland gaining the upper hand in extra time. But the rearguard held firm, forcing the tie to penalties.
That defence will have to be immaculate again if Poland are to have a chance of progressing because they have offered little up front.
They have scored two goals fewer than any other team in the last eight with hitman Robert Lewandowski, the leading scorer in Euro 2016 qualifying with 13 goals, mustering just two attempts on target so far, both in the last match.
The captain's opening penalty in the shootout, which left the goalkeeper stranded as it flew into the top right corner, could be the confidence boost he needs.
It is the scintillating left winger Kamil Grosicki who presents the biggest danger for Portugal's ageing but experienced defence led by 33-year-old Pepe.
For Polish coach Adam Nawalka, the Ronaldo factor presents a tactical conundrum. Is he prepared to press high in search of a goal, knowing that a wrong step could unleash the Portuguese counter-attack, or does he sit back and risk becoming just a spectator to another Ronaldo masterclass?
Whoever wins on Thursday will play either Wales or Belgium next, seen as the easier route to the final with hosts France, world champions Germany, Italy and surprise quarter-finalists Iceland on the other side of the draw.
(Editing by Clare Fallon)
