He is the outstanding racing driver since the Second World War Niki Lauda on Michael Schumacher

"He is the greatest. Nobody will ever beat him, as long as we are alive," said Lauda, who played down Schumacher's dubious sporting ethics.

"Every driver has to have the same determination. There are no rules really. All you have to do is win."

Coulthard, the German's long-time rival added: "He is the greatest all-round racing driver this sport has seen."

Interview: David Coulthard

Schumacher will retire after driving in Sunday's Brazilian Grand Prix, where he will clinch an eighth drivers' crown if he wins and championship leader Fernando Alonso of Renault fails to score a point.

And Lauda believes even Schumacher's current record haul of seven world titles may never be broken.

"He is the best - [Argentine Juan Manuel] Fangio was [on] five for 30 years and Michael is seven now," added three-time world champion Lauda.

It has been frustrating at times because Michael has taken what have been clearly defined rules of the sport and pushed those lines David Coulthard

"He is the outstanding racing driver since the Second World War."

Despite Schumacher's success, many have been critical of the 37-year-old's sometimes controversial tactics in pursuit of victory.

At the 1994 Australian Grand Prix he crashed into championship rival Damon Hill, ruling both cars out of the race but sealing the world title, while a similar move on Jacques Villeneuve failed three years later.

But Lauda has no problem with Schumacher's approach to the sport.

"Michael is doing exactly what all the others do," he said. "The only problem is he was caught a couple of times."

Coulthard is critical of Schumacher's contribution to motorsport

Coulthard has had a number of run-ins with Schumacher, but the Scot said racing against him had enhanced his own career.

"He is a controversial driver because of some of the showdowns he has had with Damon Hill and Jacques Villeneuve," Coulthard told BBC Radio Five Live's Sportweek. "It is exciting to race against him.

"Unquestionably I would rather have raced in this period against the most successful driver in the history of the sport.

"It has been frustrating at times because Michael has taken what have been clearly defined rules of the sport and pushed those lines.

"All the time it has pushed the boundaries of what would be considered the normal sporting ethics of motor sport."

Red Bull driver Coulthard also believes Schumacher could have done more to help the sport, and used the US Grand Prix fiasco in 2005 as a prime example.

The seven teams using Michelin tyres could not race because of safety concerns, and only the six Bridgestone-backed cars - including Schumacher's Ferrari team - were able to race.

"Michael didn't really fight to support the rest of the drivers to make sure we could put on a good show for Formula One because it was an opportunity for him to win a Grand Prix," Coulthard said.