Both teams have taken just one point from their first two Group G encounters, and a draw between Germany and the United States in the other pool fixture would make the outcome in Brasilia irrelevant.
Portugal's task is particularly difficult as a 4-0 defeat to Germany in their opener has left them with a vastly inferior goal difference, and they need a huge goal swing, as well as three points, if their World Cup is to be extended until at least the last 16.
Indeed, Paulo Bento's men are somewhat fortunate to have another chance of reaching the knockout stages as they were on the brink of elimination when trailing the United States 2-1 in the dying stages of Sunday's meeting.
But Silvestre Varela's header deep into injury time rescued a vital point for Portugal, keeping their hopes alive.
Portugal talisman Cristiano Ronaldo has struggled for form and fitness throughout the tournament and he drew criticism from some quarters for his display against the United States, but it was the Real Madrid forward's superb delivery that led to the equaliser.
The late rally may still prove to be in vain, but centre-back Ricardo Costa is remaining confident despite the odds being stacked against Portugal.
"We need to win," he said. "In our mind is that goal, scoring enough goals to move on.
"(We) have a game... to beat Ghana and maintain the hope of going to the next round."
Bento's options are boosted by the return of centre-back Pepe from suspension, while full-back Andre Almeida (hip) and striker Helder Postiga (thigh) will continue to be monitored after undergoing scans this week.
Ghana's preparations have been blighted by a series of off-field issues, with Ghana Football Association president Kwesi Nyantakyi strenuously denying knowledge of alleged attempts to fix national team matches, while a payment dispute involving the team's players has also proved an unwelcome distraction.
Despite those problems, Ghana can take confidence from a plucky 2-2 draw with Germany last time out, in which Kwesi Appiah's men had led 2-1 before Miroslav Klose's intervention.
On paper, Ghana's chances of qualification are greater than Portugal's, due to a better goal difference, and head coach Appiah is confident his team have the right mentality to reach the knockout stages.
"Ghanaians have a strong mentality in football," he said. "We always believe we have to fight to the end never mind what happens initially."
Ghana will be forced into one change as midfielder Sulley Muntari is suspended.
