Daniel Ricciardo will drive on Tuesday with Spanish Grand Prix race-winner Max Verstappen taking over the day after for the two-day test.

Renault's upgraded engine is predicted to deliver a power boost that could be worth up to four tenths of a second per lap, which would put the team even more in the mix with Mercedes and Ferrari.

Red Bull boss Christian Horner praised the work that Renault had been doing, as he talked with confidence about what potential there was still to come.

"With what's in the pipeline for the coming races, there's a lot of reason for optimism," he said.

"I think if we get what's advertised then it's going to put us in a position to at least race Ferraris every weekend, and then hopefully we can get into trying to close that gap down to Mercedes at certain circuits.

"Daniel [Ricciardo] qualified within 0.65 seconds of Lewis Hamilton here, which is the closest I think anybody has really been in the last 12 months.

"At a track like this, that is really encouraging. So I think if we can find a few tenths on the power unit side it's only going to be gratefully received."

Red Bull's decision to use Ricciardo and Verstappen means it is one of two teams to run just race drivers, the other being Haas.

Every other outfit has split duties between its regulars and a youngster.

Barcelona test line-up