With Jean-Eric Vergne set to be retained by Toro Rosso for a third season in 2014, Tost indicated that, given the team's success with Ricciardo, another racer from Red Bull's young driver programme could fill the vacant seat alongside the Frenchman.
“As to who will replace Daniel at Toro Rosso in 2014, we will now look at all our options and make a decision at a later date, as there is no immediate need to rush,” said Tost.
“When Dietrich Mateschitz acquired the team that became Toro Rosso, his stated aim was that it should be the final step in the training of young drivers, with the eventual goal of graduating to the ‘senior’ team.
"Daniel’s move thus vindicates the work of the Red Bull Young Driver Programme and also proves that we at Toro Rosso have given him a good racing education.
“We are very pleased to see him make this move, which means he will follow in the footsteps of Sebastian Vettel.”
Red Bull have a number of talented young drivers on their junior team roster, the most experienced being Antonio Felix da Costa.
The Portuguese driver is a multiple race-winner in Formula Renault 3.5 and tested for Red Bull at this year’s young driver test at Silverstone. GP3 drivers Carlos Sainz Jr and Daniil Kvyat were also given F1 run-outs at the same test.