Daniel Ricciardo is the Toro Rosso driver leading the race to step up to Red Bull next season, according to his team boss Franz Tost.
Earlier this month, Red Bull advisor Helmut Marko gave his support to Ricciardo, saying he is the "better" driver to replace Mark Webber should the 36-year-old leave at the end of this season.
Ricciardo has proven to be Toro Rosso's best driver in the opening stint of this year's Championship, scoring seven points to Jean-Eric Vergne's one.
Added to that, the 23-year-old has also outqualified his team-mate four out of five times while also securing the team's only top-ten grid position of the campaign.
"Well, performance is all that matters and you definitely can see that Daniel with 11 races more under his belt - which is more than half of a season - is probably in a better situation," Tost told the official F1 website.
"Right now he has the upper hand, which we have seen in Barcelona. But that is a snapshot right now. Generally I would say that both would fit into the Red Bull concept."
However, the team boss has mixed feelings about whether either driver is ready for the job.
"At the moment I would answer with a 'yes and no'.
"Both would have to demonstrate an exceptionally good second half of the season, because don't forget we are speaking about the World Champions, so the requirement profile is quite different to being with a team like Toro Rosso.
"But don't get me wrong, both are on a very good path and everything will depend on the next couple of months as to whether one of the two of them - should the need be there - qualify for Red Bull Racing."