The 39-year-old has more caps and more goals than anybody else in men’s international football history, with 130 strikes in 212 games.
He is in Portugal’s squad for Nations League games with Croatia and Scotland.
But Ronaldo comes into these games after a hugely disappointing Euro 2024 campaign where he failed to score and many felt he held the team back.
The Manchester United and Real Madrid legend now plays in Saudi Arabia for Al-Nassr.
“When the time comes, I’ll move on,” he said.
“It won’t be a difficult decision to make.
“If I feel like I’m no longer contributing anything, I’ll be the first to leave.”
The five-time Ballon d’Or winner says he “never considered leaving the national team” despite the post-Euro 2024 criticism.
Ronaldo and team-mate Pepe, aged 41, were the two oldest players at Euro 2024.
After their Euros exit, former Portugal international Jose Fonte told BBC Sport: “They probably know it’s the end of the line in the national team.
“They’ve done so much for Portugal.
Sometimes you just have to give your place to the young boys coming up.”
Pepe has retired, with Ronaldo saying the defender “left through the front door”.
But the forward has opted to carry on.
“People’s expectations of the national team were too high,” added Ronaldo on their quarter-final exit to France on penalties.
Last month he said: “I don’t know if I will retire soon, in two or three years, but probably I will retire here at Al-Nassr.
“When I leave the national team, I won’t tell anyone in advance and it will be a very spontaneous decision on my part, but also a very well thought-out one.”
