Friday 22 August at 09:53 : Sebastien Bourdais must still prove he deserves to retain his Toro Rosso race seat beyond 2008, team co-owner Gerhard Berger insists.

Franz Tost is the Faenza based team's principal, and Red Bull's Dietrich Mateschitz is also a part-owner, but Berger - a former ten time grand prix winner - takes a leading role in the key decisions of the team.

One of his greatest interests is the occupants of the cockpits. He believes Sebastian Vettel is a huge talent, but will lose the German to parent team Red Bull Racing in 2009.

In the other STR single seater at present is Sebastien Bourdais, who received his F1 break this season with Berger's blessing after years of dominance in Champ Car.

But Berger openly admits that the 29-year-old Frenchman has not yet proved he belongs in F1 long-term.

He told Formule 1 Race Report that identifying talent suitable for F1 is only a 50 per cent guarantee that the driver will prove his worth.

"During the season it can turn up that it didn't work, because only then do you see them under pressure," he said.

The Dutch magazine asked Berger if the rise and demise of Scott Speed is an example of a promising driver stumbling at F1.

"Exactly," he said. "Scott was in the wrong place at the wrong time. But I hear he is doing well in America and I'm pleased to hear that."

So could Bourdais follow the Californian back to America following a short F1 tenure?

"We gave Sebastien half the season to adjust to formula one," Berger says. "That is over now, so he has to show that he deserves to be driving here. I think he can do it."