"We got him (Ricciardo) because, among the many possible choices, we were convinced that he was the best," team boss Christian Horner told Italy's La Gazzetta dello Sport.
"We knew from the test data and the simulator that he was strong. We expected performance close to Sebastian, but not what we saw in the first four races.
"And the more he integrates, the stronger he will get," added Horner.
Meanwhile, as Gerhard Gribkowsky prepares on Friday to give potentially explosive testimony to the Munich trial, Horner backed Bernie Ecclestone to keep running formula one amid the corruption scandal.
"Bernie has done an amazing job and F1 needs him more than ever," he said.
"At this time it would be a disaster if he wasn't here anymore," added Horner, who has regularly been named as Ecclestone's preferred successor.
"I am honoured," said Horner, "but my focus and my commitment is to Red Bull. And, anyway, no one can just replace Bernie."
Finally, Horner revealed that he has spoken to his former counterpart Stefano Domenicali after his Ferrari exit.
"Yes, he was in the Dolomites," the Briton revealed.
"I'm very sorry about it, because he was someone you can trust. His role at Ferrari was not easy and I wish him all the best," added Horner.
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