Red Bull team boss Christian Horner believes beating rivals and leaders Mercedes in Spain is his team's last chance of staying alive in the title race.
The Mercedes pair of Nico Rosberg and Lewis Hamilton have 79 and 75 points with the team winning all four races of the season so far. Red Bull's world champion Sebastian Vettel and teammate Daniel Ricciardo have 33 and 24 points.
"We've got to [beat them in Spain] if we're going to make a championship of it," Horner told Sky Sports F1. "We've got to take the fight to them. We're going to give it everything. I believe we can take the fight to them, we just can't concede too much more ground."
Button wants more
Former world champion Jenson Button, meanwhile, wants his team McLaren to implement a drastic upgrade for Spain as its current form is "not good enough".
McLaren has fallen off the pack and sit behind Mercedes, Red Bull, Force India and Ferrari on the table with 43 points.
"We've got some upgrades coming, but we were a lot further behind [in China] than we were in the last race," Button said. "We just aren't quick, I don't think people brought that much so I don't know what we are doing really. China was disappointing for the whole team, when everyone works hard and you have such a bad result it's tough, especially for the guys back in the factory.
"Hopefully they can stay positive and keep updating the car because at the moment this isn't good enough."