The 31-year-old forward, warming up for his side's Group F opener against Iceland on Tuesday in Saint-Etienne, made his first appearance with Portugal this summer in Lisbon on Wednesday night.
"It was just a friendly and even though we won 7-0, it doesn't mean anything," Ronaldo was quoted as saying by AS newspaper.
"We must keep our feet firmly on the ground. The team played very well and we are all physically well.
"We are on the right path but we have to keep our feet firmly on the ground."
Ronaldo started and scored Portugal's opening two goals before being replaced by Nani in the 46th minute.
"I would have liked to have played more but it was better to manage my time on the pitch and give others an opportunity to play," he said.
The Portugal captain was not fit at the World Cup in Brazil two years ago due to a tendonitis problem and his national team failed to progress from the group stages.
Ronaldo was bothered by muscular problems at the end of this season with Real Madrid yet helped his club beat Atletico Madrid in the Champions League final in Milan last month.
He finished the campaign with 51 goals in 48 games in all competitions for Real.
"I'm not at my best," Ronaldo admitted. "But there is still a week to go before we start Euro 2016 and I have time to improve."
Portugal reached the semi-finals four years ago but were eliminated by Spain on penalties and Fernando Santos's men are looking to go all the way in France.
"The group stage is the most important thing and then we will see," Ronaldo said.
"We have to take it one step at a time.
"After their opener, Portugal take on Austria on June 18 in Paris and end the group stages four days later against Hungary in Lyon.
(Reporting by Cindy Garcia; Editing by Amlan Chakraborty)
