Japanese driver Takuma Sato has ruled out any reserve role with either of the Red Bull-owned Formula One teams this season after failing to secure a race seat with Toro Rosso.

"I am no longer in negotiation with the Toro Rosso or Red Bull teams about their third driver positions," Sato said on his personal website (www.takumasato.org).

"I am very disappointed that we were not able to come to an agreement with them, but you never know what is around the corner," added the 32-year-old.

Japan's most successful Formula One driver has been out of F1 since his Honda-backed Super Aguri team folded last April.

The third driver role is marginal this year. Testing is banned during the season and there is no scope to get behind the wheel at race weekends unless the regular driver is unable to compete.