Belgium, the Republic of Ireland and Sweden, meanwhile, are still in contention to join Group E winners Italy in the last 16.
Ronaldo missed a penalty and other chances as Portugal were held 0-0 by Austria to leave Fernando Santos's men third in Group F with just two points from two games.
However, victory will guarantee Portugal top spot in the group and avoid a much tougher side of the draw containing hosts France, world champions Germany and England.
"Ronaldo is a player who scores a lot of goals and I’m sure he will score in the next game against Hungary," said Santos.
The former Porto, Benfica and Sporting Lisbon boss insists he does not care how Portugal win as long as they pick up three points.
"We’re sad but we have things in our own hands.
"It doesn’t matter if we play better or ugly football."
Ronaldo has another chance to become the first player to score in four different European championships.
Forty-year-old goalkeeper Gabor Kiraly stands in his way, though, for a Hungary side assured of their place in the knockout stages after a 30-year wait to qualify for a major tournament.
Hungary shocked neighbours Austria 2-0 in their opening game before a late own goal handed them a 1-1 draw with Iceland.
"Who would have thought that we'd be top of the group with four points and that Portugal would need to win to qualify?" said Hungary boss Bernd Storck.
"We have nothing to lose, Portugal have to win."
All is to play for in the other game in Group F with a win also good enough to take either Austria or Iceland, on their debut in a major finals, through to the knockout stage.
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