Heinz-Harald Frentzen has been dubbed too soft to succeed in Formula One by his old boss Frank Williams.

The German, who drove for Williams in 1997 and 1998, will make his grand prix comeback at March's season opener in Australia after re-joining Sauber.

Frentzen was dumped by Williams after scoring just one win in his two seasons with the British-based team.

And his former boss said: "I don't know of any other driver who has such a fantastic feeling for the car he drives as Frentzen does.

"But Heinz-Harald is a very sensitive character and not hard enough for this business."

After being dropped by Williams, Frentzen rebuilt his reputation at Jordan, winning twice and finishing third overall in the 1999 championship.

But he was controversially axed midway through the 2001 campaign.

Frentzen then drove for the now defunct Prost outfit before joining Arrows, but left last season when Tom Walkinshaw's team ran into money trouble.

The 35-year-old has now returned to Sauber, where he started his career in 1994.