Three-time F1 World Champion Niki Lauda has warned Ross Brawn that he and Mercedes will need to sign a driver as good as or better than Jenson Button to replace the 2009 title-winner – or else they will have little chance of successfully defending their hard-fought crowns.

Having risen phoenix-like from the flames in the wake of parent company Honda's sudden and shock withdrawal last winter, Brawn GP went on to stun seasoned paddock observers in 2009 by coming out of the blocks in storming fashion in Melbourne with a dominant one-two for Button and team-mate Rubens Barrichello in the Australian Grand Prix curtain-raiser – and just under seven months later, they had wrapped up both championship titles to boot.

Whilst recognising and acknowledging the undisputed magnitude of that achievement, Lauda fears Brawn may yet come to regret letting Button slip through his fingers, and contends that the British star – who jumped ship to join compatriot and fellow world champion Lewis Hamilton at McLaren-Mercedes, after months of protracted salary negotiations with the Brackley-based outfit failed to reach a satisfactory conclusion – is fully deserving of the drivers' trophy, regardless of his off-colour mid-season slump.

“Worthy or unworthy is the wrong approach,” the Austrian opined in an interview with the official F1 website. “A world champion is a world champion. You might argue about the manner in which he won, but history has shown that in some years you have guys who win everything, and then you have guys – and I count myself among these – who win with a half point lead in the last race. There are many ways to win a championship.

“He put in a good season – starting very strong at the beginning to forge ahead and then keeping the lead through difficult times of constantly losing points, but still staying in front. He was 'nail-biting' himself to the title – at least from the outside. It is hard to say why he was losing out to Rubens – someone running on the same equipment – in the second half of the season.

“In the end it's a pointless discussion, because he was not the only one running on a bumpy performance curve; Sebastian [Vettel, Red Bull Racing rival] also had his share of poor results. In that scenario of ups-and-downs, Jenson was able to keep enough points to maintain his lead – that's why he ended up as champion and not somebody else. Yes, the 60th Formula 1 World Champion is a worthy champion.

“I am sure that Ross was not completely satisfied with Jenson's performance in the second half of the season, but if Mercedes ends up with someone not as good as Jenson, then they've drawn the short straw. Ferrari's pairing of Alonso/Massa and McLaren with their two British champions will be very, very competitive. We have also seen how Vettel and Webber egg each other on to top performances, so the 'Silver Arrows' will be confronted with competitors with top driver line-ups. I would not have an idea who they should take; in my opinion all the top drivers are already signed.”

Insisting that he was 'not really' surprised by Button's defection to Woking – what he describes as 'a true Ron Dennis move' – Lauda went on to suggest that it might not only be Brawn who regrets the unexpected divorce, predicting that Mercedes Grand Prix will be a force to be reckoned with indeed in the years to come. All they need now, he adds, is a top-line driver line-up to match.

“You can argue back and forth about Jenson, but one thing is undeniable,” asserted the 60-year-old, who lifted the world championship laurels for Ferrari in 1975 and 1977 and for McLaren in 1984. “What Ross formed out of the bankrupt Honda estate, in a cloak-and-dagger operation, to dominate all the 'big boys' in the paddock, was truly phenomenal. That has never happened before in Formula 1. That is the real sensation of the season, and their winning the constructors' championship is highly deserved.