Victory over Hungary will guarantee Portugal top spot in the group.
Portugal will be relying on a drastic turnaround for superstar captain Cristiano Ronaldo to avoid an embarrassing early Euro 2016 exit against surprise package Hungary on Wednesday.
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.
With four points enough to ensure at least one of four best third-placed finishes, Ireland need to beat Italy to seal their last 16 place in Lille.
Martin O'Neill's men were swept aside 3-0 by Belgium after a promising opening performance in a 1-1 draw with Sweden.
Former Celtic manager O'Neill does not want his side to go chasing the game too early and be caught on the counter-attack as they were ruthlessly for Belgium's first and third goals.
"It's a fairly lengthy evening. We know at the end of it we have to be in front and it's a case of being very, very strong to begin with," O'Neill said Tuesday.
With a maximum six points from two games, Italy are guaranteed to progress as group winners and coach Antonio Conte is expected to make up to nine changes to his starting line-up to keep legs fresh and protect those players who are one yellow card away from a ban.
Sweden captain Zlatan Ibrahimovic can also become the first man to score in four Euros if Ronaldo fails to find the net in what could be his last international appearance.
Ibrahimovic announced on Tuesday that he will retire from international duty at the end of the Euros. Sweden must beat Belgium in Nice to make the last 16.
"The last game with Sweden in the Euro will be my last game with Sweden. So I hope it won't be tomorrow," said the 34-year-old.