Portugal boss Paulo Bento admits that he does fear Northern Ireland could cause an upset against his side.
On paper Bento's side would be expected to win their World Cup qualifier at Windsor Park comfortably but he is taking nothing for granted.
Northern Ireland's best results under Michael O'Neill have come in their toughest encounters - with a 1-1 draw in the reverse fixture in Porto and a shock 1-0 win over Russia last month - and Bento has taken note.
Speaking via a translator after his side's final training session, he said: "I expect Northern Ireland to play with a similar structure to what we saw in Porto...they are aggressive and play direct football.
"They have got quality and maybe I expect them to take on the match a bit more than last time.
"Northern Ireland have a chance, so maybe it is possible that they attack a bit
"The Russia match was another warning. We knew this match would be tough but that game and the way they beat Russia showed that they're a really strong squad. It was a warning for us."
Bento has previous experience of being frustrated in Belfast, having been an unused substitute in a 0-0 draw 16 years ago.
"Being here brings back memories of 1997," he said.
"It is the same situation for me...I was sitting on the bench then and I will be sitting on the bench here again."
He would not be drawn on Cristiano Ronaldo's mood, with reports suggesting the Real Madrid star is unhappy at the club's decision to sell Mesut Ozil to Arsenal.
Ronaldo is understood to have made his dissatisfaction with the sale clear to his international colleagues this week, but Bento was focused on Portugal's task.
"The only thing that matters to me is Ronaldo is happy to be here," said Bento.
"He will help us try to win the match. Rumours about other things are none of my business.
"If nothing abnormal takes place between now and tomorrow he will be fit and play."
Northern Ireland v Portugal is live on Sky Sports 4HD at 7.30pm