Red Bull F1 team feels progress on chassis side with 2015 car

The team currently stands fourth in the constructors' championship, 136 points behind leader Mercedes, but Horner believes the last event in Bahrain proved things are improving.

"We're definitely making progress with the car; Bahrain was actually our most competitive weekend," said Horner.

"The problem we've got is that we're running in such a compromised state, so we're not in an optimum window with the car.

"Our straight-line speeds are down and then you end up trimming wing out to try and get something sensible.

"And that hampers other things such as tyre warm-up and downforce.

"So we're not in a window with the car where we want to be at the moment, but certainly we've made significant progress."

Ricciardo's sixth place matched Red Bull's best result of the season, which the Australian also achieved in his home grand prix.

He qualified 1.261s off pole position, comfortably the best that Red Bull has achieved all year.

Horner paid tribute to Ricciardo's attitude and approach amid a difficult start to the year.

"He's no different at all [compared to last year]," said Horner.

"His attitude, his approach, his personality, his demeanour is exactly the same.

"That's great for the guys around him as well. He's not letting his head drop and I'm very impressed."