According to British magazine Autosport, the Twynholm-born driver will take that role within the RBR team only until the Milton Keynes based outfit will secure the services of New Zealand's Brendon Hartley. The latter is yet to be granted the mandatory superlicense for the F1 job, which Red Bull Racing believe it will happen within the next few weeks.
Although he retired from racing after last year's Brazilian Grand Prix, the Scottish driver announced he will be taking an advisory role within his former team through the upcoming season. In addition to that job, Coulthard also committed to a commentary role with BBC for 2009.
The testing/reserve job for Red Bull Racing has been subject to discussion ever since Toro Rosso announced Sebastien Bourdais's contract extension in early February. Red Bull owner Dietrich Mateschitz decided to give the job to Japanese driver Takuma Sato, as a compensatory measure for not naming him official STR racing driver for 2009.
The F1 veteran turned that offer down, reason for RBR to focus on their attention on young and promising Hartley. Front runner in the British Formula 3 Series and part of Red Bull's Junior Programme, the New Zealander has already completed his maiden test with the team this winter, when replacing injured Mark Webber in mid-December.
It is believed Coulthard will step down from his reserve driver role with Red Bull once the F1 caravan will make its European debut, at Barcelona.