Ronaldo, 37, spoke at a news conference ahead of his team's playoff final against North Macedonia on Tuesday in Porto, with the winner of the game going to the 2022 World Cup.
When asked if this will be his last World Cup should Portugal qualify, Ronaldo said: "I'm starting to be asked the same question. The one who is going to decide my future is me, nobody else. If I feel like playing more, I'll play, if I don't feel like playing more, I won't. I'll decide, period."
Euro 2016 winners Portugal have qualified for the last five World Cup finals, while North Macedonia's first major tournament in their 27-year history was last year's Euro 2020.
When questioned if the World Cup could be the same without him, Ronaldo said: "There is no World Cup without Portugal, here there are no individuals, we are a group.
"Tomorrow is a final and we are ready. Favourites?... I always consider myself favourite, whether [playing] at home or away.
"We already know that if we win, we will go to the World Cup, if we lose, we are out. We have a responsibility to be positive and win the game.
"The pressure always exists. I feel good, as usual. Another day that I will be ready."
"They have surprised [opponents] in many games but I believe that tomorrow they will not surprise us," Ronaldo said of North Macedonia. "Portugal will be better and we will go to the World Cup.
"For us it's also a game of [our] lives."
Portugal coach Fernando Santos agreed with Ronaldo.
"We know [North] Macedonia well and we have to respond accordingly," he said. "This may be the game of their lives, but for us it is also, and this is how we have to respond, with dedication, determination, intensity, a spirit of sacrifice and will.
"We have to win, win, win.
"We count on the unconditional support of the 11 million Portuguese people."