Sep.2 (GMM) Retiring grand prix veteran David Coulthard may relinquish his seat at Red Bull Racing before the end of the 2008 season, according to the latest whisper in formula one circles.

The rumour coincides with Red Bull junior team Toro Rosso's confirmation on Tuesday that Sebastien Buemi and Takuma Sato will be tested later this month in view of replacing Sebastian Vettel in 2009.

In a statement, Toro Rosso said the pair will get a day each at the wheel of the STR3 at Jerez following the Italian grand prix because the team is "turning its thoughts to its 2009 driver lineup".

"The time has come to try and find a suitable replacement for Vettel," Toro Rosso principal Franz Tost said.

According to the Coulthard rumour, the 37-year-old Scot would hand over to Vettel after Monza, thereby creating an early vacancy alongside Sebastien Bourdais at Toro Rosso.

The Ferrari-powered team would then be free to trial teenager Buemi, Super Aguri refugee Sato, or any other 2009 candidates - perhaps Bruno Senna - at the final four races of the season.

In terms of the current constructors' championship, however, the rumour makes little sense.

STR's Vettel was the star of the recent Valencia race, collecting three points for sixth place, but the team sits just ninth out of the ten teams -- three and six points respectively behind Honda and Williams.