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Ronaldo is playing in a record-breaking sixth FIFA World Cup, with only Lionel Messi matching that feat, but the Argentina great was the first to achieve it.

Last time out in a dramatic 2-1 win over Croatia, Ronaldo became the first player to appear in the tournament knockout stage at 41 years of age or older.

He scored from the penalty spot to drag Portugal level – his third goal of this year's finals – netting in the knockout stage for the first time at his 31st attempt.

The records have tumbled throughout this FIFA World Cup, as Ronaldo became the first man in history to score in six different editions and has netted 10 goals overall, the most of any Portugal player, ahead of Eusebio's nine.

Ahead of the Selecao's Round of 16 clash with Spain in Dallas on Tuesday (AEST), Ronaldo announced that this would be his last time appearing at the tournament.

"Yes, it's my last one [World Cup]," he said. "Let's go and enjoy it."

But when asked if this also meant his retirement from international football, Ronaldo hit back: "I will retire when I want, not when you want.

"Whether I play or I stay on the bench, the influence will not change.

"I am not the player I used to be, but I am not doing too bad. I keep scoring goals. If I can't score, it will be another team-mate to score, and we hope to go to the next round. The mission is to advance, not for me to score."

Ronaldo is Portugal's all-time leading goalscorer, having netted 146 goals for his country.

Overall in his career, he is up to 976 goals with club and country and is chasing down the 1,000 mark.

But Ronaldo showed his pride at the longevity of his career, while also pointing out that questions over his future are nothing new.z

"It's been like this since I was 18; it is not going to change," he added. "I always put body and soul [into] trying to get our goals – playing or not playing, I will always have an important role to play.

"As I said before, I will stop when I choose, not when you choose. You always ask the same question. I don't want to draw attention to this because it is less important.

"People question me starting at 41? You have been trying to kill me for the past 23 years. But you must have seen that is not worth it, it's a waste of time, but you try and try and try and try and try. I am so used to this.

"I even say thanks for the attacks I feel after I turned 40… the criticism is how you grow, so thank you for doing this.

"I am not going to be more Cristiano Ronaldo or less because I win the World Cup. Age gives you maturity and experience to see how relative things can be."

Spain and Portugal have met five times previously at major tournaments, with three of those meetings ending in a draw with one win each.

Its most recent knockout-stage meeting came in the UEFA Euro 2012 semi-finals, which Spain won on penalties.