Coach Paulo Bento has engineered a remarkable turnaround, improving the side's morale after replacing the sacked Carlos Queiroz in September.
He took charge after an embarrassing 4-4 home draw with Malta and a 1-0 defeat in Norway but subsequent wins over Denmark and Iceland have pushed Portugal, who are equal on goal difference with the Group H leaders, within three points of Norway.
"It is a key opportunity to go first in the group," Bento told a news conference. "We are under pressure but it is a much better kind of pressure than what we had back in October."
Ronaldo has been on fire at Real Madrid this season, netting 40 goals to set a La Liga record, and the Portugal captain and the world's most expensive player said he had one last job to do before going on holiday.
"The season is not over yet. I have an important game to play for Portugal and I want to win it," he said.
"He (Ronaldo) is world class, we must allow him very little space and always have to be on top of him," Norway coach Egil Olsen said.
