Timo Glock has warned that Toyota must be wary of the challenge from Ferrari, McLaren and BMW Sauber despite the Japanese manufacturer introducing a new front and rear wing his weekend.
Toyota is currently the closest challenger to Brawn in the Constructors' Championship, but Glock believes that the team must keep pushing hard with its development program to stay at the front.
"We have to watch out for McLaren, BMW and Ferrari as they all come with a big package," Glock told AUTOSPORT. "I hope that we can at least stay where we are and in the perfect world make another step to Brawn and get ahead of Red Bull again.
"We have a nice package, but it's really tricky to say how much quicker it will be. But we have a good development program since the start of the season and it should not be too bad."
Glock added that a strong performance at the Spanish Grand Prix will be a good indicator of how Toyota will perform for the rest of the season. However, he expects there to be a lot of major developments brought in by all the teams throughout the season.
"Definitely," he said when asked if this is a crucial race. "But I think there will be more races for teams to catch up. The development with the new rules is bigger and bigger, whereas last year it was just small stuff because the cars were already maxed out. The new rules open up different ways of development and there will be more races where we will see teams making a big step.
"Barcelona is traditionally the benchmark of where the teams are and the first development shop, but there will be others."
The German believes that despite the team missing out on a potential victory in the Bahrain Grand Prix two weeks ago, his race-leading performance was a boost to his confidence.
"It was good fun to go into the first corner with no one in front of you in clean air," said Glock. "You can get into your rhythm. At the beginning I could see Jarno fighting with Lewis and I was just concentrating on pushing and being consistent. in the end, there is not much difference to leading a GP2 race!"
"I felt really comfortable in the car, but from lap 12 everything turned around and I struggled a lot. We still don't understand why I was six-tenths slower than Jarno and the car was out of balance."