Gerhard Berger selling his stake in Toro Rosso was based on a belief that the team might struggle next season.

Red Bull owner Dietrich Mateschitz announced on Tuesday that he was buying back the 50 percent stake in the team he sold to the former F1 driver ahead of the 2006 season.

Seen as the 'junior' outfit to Red Bull Racing, Toro Rosso nevertheless enjoyed the better season in 2008 and finished sixth in the Constructors' Championship.

They also scored their first victory when Sebastian Vettel took the chequered flag in the Italian Grand Prix at Monza.

Explaining his decision to sell, Berger said that he doubted the Faenza-based outfit could make further progress up the grid given next year's rule changes.

The 2009 season sees the introduction of Kinetic Energy Recovery Systems (KERS), the re-introduction of slick tyres and aerodynamic changes designed to reduce downforce.

He told autosport.com: "The new rules leave no room for improvement for a small team as STR.

"Also, Dietrich's interest will focus on Red Bull Racing, therefore the support for STR will become smaller and prevent the team from improving further from sixth. I don't want to decline, that is not in my nature."

Berger was also quick to deny that his decision to sell was based on Toro Rosso's driver choice for 2009.

The team have yet to announce their line-up, although the website also claimed that Sebastien Buemi and Takuma Sato are favourites to land the drives.

"It has nothing to do with that," Berger added.