Webber's decision to announce a switch to Porsche's new sportscar programme appeared to catch his Red Bull bosses by surprise, with team principal Christian Horner telling British media this week that his team would only replace him if it could secure a better driver.
With Webber now turning his back on Formula 1, Red Bull will have to decide on who will line-up alongside Sebastian Vettel in 2014 - with the leading contenders for the seat being Kimi Raikkonen and Toro Rosso juniors Jean-Eric Vergne and Daniel Ricciardo.
Red Bull issued a statement on Thursday that thanked Webber for his contribution to the team, but also made it clear that the decision on who will replace him will "not be made until later in the season."
Horner added: "I am sure Mark thought long and hard before making what has no doubt been a very difficult decision.
"His achievements in Formula 1 are extensive and I am sure he will continue to push hard and build on that record until the end of the season.
"We support Mark's decision, he has been an excellent addition to the team since joining us in 2007 and we wish him all the best in the next stages of his career."