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.
"I would doubt that extremely. He will regard himself as the best player in the world and he proves it every time he goes on the pitch," said the former Shamrock Rovers manager.
"His aim is to prove that every time. He is a player who has the freedom of the pitch - he's not just a threat to whoever plays at right-back, he's a threat to the whole back four.
"It's not just a case of can we get someone to stifle him in that area of the pitch because he will just come to another area to get the ball."
The identity of Northern Ireland's right-back, who will be nominally tasked with marking Ronaldo, will have taxed O'Neill.
Aaron Hughes, who excelled in the 1-1 draw in Porto earlier in the campaign, is out injured, as is his likeliest stand-in Craig Cathcart.
MK Dons defender Lee Hodson is a specialist right-back, but the leap from League One may be too great, while the versatile Alex Bruce has yet to play a competitive international.
That means a possible recall for Chris Baird, who has plenty of experience but is currently unattached following his release by Fulham.
"If I had to call on Chris I know he has got the know-how and the experience to be able to deal with it," said O'Neill