Both teams need a victory and a USA defeat to have any chance of advancing to the last 16 - a scenario which should ensure excitement at the Estadio Nacional Mane Garrincha
Portugal coach Paulo Bento has plenty of selection worries ahead of Thursday's decisive match against Ghana, as he will probably have to make do without the services of a number of regulars.
Fabio Coentrao was forced to pull out of the squad after the loss against Germany, while Rui Patricio, Hugo Almeida, Andre Almeida and Helder Postiga have also been plagued by injury problems since the start of the tournament.
Beto is therefore expected to start between the sticks again while Miguel Veloso could fill in at left-back, thus making room for William Carvalho to start in midfield - although Ricardo Costa also remains an option in defence.
With both Postiga and Hugo Almeida unlikely to be match-fit in time, Eder is expected to feature from the start this time around after coming off the bench in Portugal’s previous two group stage matches.
Ghana coach Kwesi Appiah, meanwhile, has no noteworthy injury problems as the Africans aim to book their ticket for the round of 16 after a disappointing start to the tournament.
Kevin-Prince Boateng and John Boye picked up minor knocks in the draw versus Germany, yet both have been given the green light for the match against Portugal.
Appiah will have to make at least one change to his starting line-up however, as AC Milan’s Sulley Muntari is unavailable due to suspension, following his two yellow cards earlier in the competition.
His position will be taken by either Michael Essien or Emmanuel Agyemang-Badu, with the former sitting in pole position to feature from the start.
Furthermore, Appiah will have to choose between either Boateng or Abdul Majeed Waris – who has recovered from injury – to partner Asamoah Gyan in attack.