With the likes of Ronaldo, Nani, Silvestre Varela and Joao Moutinho in their ranks, Paulo Bento's side have proved quite a draw - with Windsor Park selling out for the first time in the current World Cup qualifying campaign.
Northern Ireland's morale-boosting win over Russia last month may also have contributed to that but the chance to see some of the world's best players up close will have had a big impact on sales too.
Yet O'Neill accepts his side would not be able to match their illustrious opponents in a free-flowing contest and is intent on being effective rather than entertaining.
"We don't want it to be a beautiful game of football if I'm 100 per cent honest," he said.
"That's not how we're going to excel. They'd love the game to be open: they love space, they love to be able to play on the counter attack.
"It's important they have a difficult night and that they know from the word go that they're going to have a difficult night.
"I think it would be foolhardy of us to go and play a really open game and say to Portugal 'Come and play us, you attack us and we'll attack you'."
As ever all eyes will be on Ronaldo, with the added interest of it being his first appearance since Gareth Bale's arrival at Real Madrid - a move which reportedly saw the Welshman replace his new team-mate as the most expensive player in the world.
O'Neill is certain he will feel no extra motivation because of that.
Source: PA
Source: PA