Red Bull are waiting on a Renault upgrade that has been delayed for reliability reasons.
In Barcelona, the former champions took a clear step closer to runaway pacesetters Mercedes and Ferrari.
"We closed more than 60% of the gap," Red Bull official Dr Helmut Marko told newspaper Salzburger Nachrichten.
He admitted that the team are hoping for another big step in time for the Red Bull-promoted Austrian Grand Prix, but that also depends on whether the Renault upgrade will be ready by then.
"Naturally we are hoping that something will come before Austria," he said.
The Austrian Grand Prix takes place on July 9.
