After being forced to qualify via the play-offs for the tournament, the Portuguese are not being talked up as potential champions, especially as they share Group B with Germany and the Netherlands.
"We know we are in the group of death with Germany, Netherlands and the team who knocked us out [to the play-off] in the qualification phase, which was Denmark," Ronaldo said in an interview published by Real Madrid's sponsor Bwin on Tuesday.
"Those are going to be some very tough matches but I am confident we will go past the group phase. I know we will not be favourites. Even better," he added.
Portugal faced whistles from their fans after a disappointing 0-0 home draw against Macedonia on Saturday left question marks over the team's form.
They play Turkey in a friendly at the weekend, their final test before leaving for Poland where the 27-year-old Real Madrid forward's trickery, pace and ferocious shots are expected to be a highlight.
While he would love to captain Portugal to a first major success, Ronaldo said he expected Spain to retain their title.
"I don't think there will be surprises in this Euro, Spain are very strong and there are teams right behind them which are also very tough so I don't think there will be any surprises," he said.
Having missed out on the trophy in Euro 2004 when hosts Portugal were beaten by Greece in the final, Ronaldo's form will be vital.
Ronaldo scored only one goal in each of the last three major international tournaments - Euro 2008 and the World Cup finals in Germany and South Africa.
