Cristiano Ronaldo will not want to stop without a World Cup win that allows him to emulate eternal rival Lionel Messi, the Portuguese’s former Manchester United team-mate Kleberson has told GOAL. A man who knows all about the mindset of an all-time great has also boldly predicted that evergreen CR7 could play on until the age of 50 if he really wants to.Ronaldo has already passed his 40th birthday and signed a contract extension with Saudi Pro League side Al-Nassr that will take him to the summer of 2027. He has been showing no sign of slowing down and is expected to grace another major international tournament this summer.The five-time Ballon d’Or winner remains captain of his country, with a record-setting tally of 143 goals to his name, and is as hungry as ever for tangible success. He saw Messi conquer the world with Argentina in 2022 and will be determined to ensure that he does not bow out without a similar entry being made on his glittering CV.Quizzed on how desperate Ronaldo will be to capture a global crown, 2002 World Cup winner Kleberson - speaking in association with BetVictor Online Casino - told GOAL: “Inside of him he probably feels ‘gosh, I have to win the World Cup, I can’t finish my career like this’.“He has to work hard. It’s not just him, it’s other players. Neymar also is probably thinking ‘Messi has a World Cup, I don’t’. [Erling] Haaland as well, he might not get a World Cup. It’s inside players, inside these top players. “Look at Adriano - he’s a big name in Brazil, in Italy he played at a great level, but he hasn’t won the World Cup. The World Cup is sometimes fair, sometimes unfair. I believe those guys look at me and think ‘oh my gosh, I can’t believe Kleberson has a World Cup and I haven’t!’ I don’t have five Ballons’ d’Or, but I have won the World Cup!”Looking for smarter football bets? Get expert previews, data-driven predictions & winning insights with GOAL Tips on Telegram. Join our growing community now!Kleberson got to witness Ronaldo’s initial rise towards superstardom at close quarters when joining Premier League giants United in the same summer of 2003. Asked if it was clear back then what CR7 would become, the ex-Brazil international said: “It’s all down to him. We knew that he was a good player. You could see that the kid was really good - great with the ball, good personality. “But to look at him and be like ‘five Ballons d’Or, plays in finals, wins everything’... he has proved himself over a long period. It’s not like one or two seasons. If you take my career, I had my best moments between 2000 and 2003, then I got my injury at Man United. I had great moments, played at a good level with good players. Then I got unlucky with injuries and didn’t get time to get back to that level until about 2008 to 2010. Then it went down again. “Cristiano is still the same. He is still getting titles and trophies. I’m so glad to have been able to work with him in the beginning because I’m happy to see how he has grown as a man, with his family - he’s taken care of his mum, his sister. He has a great story in football.”Add GOAL.com as a preferred source on Google to see more of our reportingThat fairytale may still have several more chapters to be written, with Ronaldo offering no indication that imminent retirement is in his thoughts. He is being tipped by some to play on to Euro 2028 and beyond.Asked if Ronaldo could continue towards the age of 50, Kleberson said: “With this kid, I can’t rule anything out! I met him when he was 17/18 years old, in 2003. We talked a lot because we wanted to speak Portuguese. We could see the things that he wanted in his life, and he hasn’t changed that. He is still the same. “If there is something that Cristiano Ronaldo has, it is mental strength. His mentality is so powerful. Then he takes care of himself a lot - his body, the way he plays. “When you watch him now, he is not like Cristiano Ronaldo of years ago, but he still has an impact. We can say ‘it’s the Saudi league, it’s not a great league’, but you can see that he plays at a good level. He is one that could move to MLS in the future. If he wants to play at 50, he can do it! He’s in great shape.”Ronaldo is currently chasing down 1,000 career goals, with that remarkable milestone very much within reach. He has also expressed a desire to play alongside his son Cristiano Jr at some stage, with it important for a player of his calibre to continue setting targets that keep his competitive fire burning after already achieving so much.