Niki Lauda feels Michael Schumacher will be looking on his return to Formula One as "nothing more than an interesting experiment".

Lauda knows what it takes to make a comeback as he spent three years in retirement before hitting the track again in 1982.

The Austrian won the third grand prix of that season, and went on to claim the third of his world titles in 1984.

Yet whilst Lauda returned for the long haul, he is confident that is far from the aim of Schumacher, who replaces the injured Felipe Massa at Ferrari, starting with the European Grand Prix in Valencia on August 23.

"He was never able to detox himself of the racing bug, as we have seen with his on-track motorcycle activities," said Lauda, speaking to the official Formula One website.

"In my opinion he retired at the end of the 2006 season because he couldn't see a real challenge - and probably he regretted his decision.

"Now he's got the unique chance to step in for the injured Massa to help his former team, and to find out for himself how competitive he still is.

"This is something that would also interest me, because this hunger for competition - for the adrenalin rush - never dies. It's in our DNA.

"And the situation as it is now at Ferrari, with a recovering Massa and an available cockpit, gives him the chance to explore how far he is off the top.

"That is a question that always puzzles a top driver like he was.

"For Michael it's nothing more than an interesting experiment."

Although now 40, Schumacher proved his fitness by completing a full day of testing in a 2007 Ferrari a week ago.

The only concern for the seven-times world champion is whether his neck, injured in a bike accident in Spain in February, can withstand the rigours of a full grand prix weekend.

That will be determined next week when Schumacher undergoes tests, with 60-year-old Lauda adding: "Forget about the age.

"He is fit, he's undergoing rigorous training, and mentally he is taking up the challenge.

"Basically, he has to focus mainly on the muscles that are called on in an F1 car and, of course, the neck.

"But that should be manageable in the next two weeks. In the end the final word will be with the doctors, to decide whether he is in the physical state to race."