Christian Horner says the timing was not right for Red Bull Racing to try and hire Fernando Alonso for next season.
The Milton Keynes-based team confirmed Sebastian Vettel will replace David Coulthard at the team in 2009, ending speculation about a possible move by Alonso from Renault.
Horner said the two-time champion was never an option for the team because of the current situation of the team and the driver.
"That was never an option," Horner told reporters in Germany. "Sebastian has been a member of the Red Bull young driver programme for many years now and he had demonstrated obvious potential.
"So after David announced his retirement it was an easy and natural decision to replace him with Sebastian.
"Fernando is a fantastic driver, I have got huge respect for him. I think he is one of the best three in the world, but the timing wasn't right for Red Bull Racing and him.
"It's early in the year to have both drivers confirmed but we decided to have stability in the team, to give clarity to the engineering staff. Now is the best time to make a commitment to what we knew was a 99% certainty anyway, and focus on the future."
Horner revealed, however, that Red Bull would have only considered Alonso had they not hired Vettel.
He added: "For us the only other driver we would have considered other than Sebastian was Fernando, but as I said, the timing wasn't right for either party in terms of what they were looking for out of a potential relationship."