Marcus Ericsson says he has worked hard to become Sauber's most competitive driver.

Early in 2015, it was the Brazilian rookie Felipe Nasr with the firm upper hand at the Hinwil based team.

It caused Swede Ericsson, who moved to Sauber after debuting for the ill-fated Caterham team, to re-focus.

"The car was fast but I was not," the 25-year-old told Brazil's Globo. "It was a very difficult start to the year for me.

"Basically I changed my way at looking at the whole weekend," Ericsson explained, revealing how he turned the situation around and is now consistently outpacing Nasr.

He not only worked harder with his engineer, but also looked carefully at the 'non-driving' aspects of formula one, including fitness and also mental health.

"I count on professional help," said Ericsson. "I attend the Formula Medicine clinic in Italy, working on several areas."

Formula Medicine is run by Dr Riccardo Ceccarelli, who has been working with F1 drivers for years, including as Toyota's doctor.

"Marcus is now more mentally mature," Ceccarelli said. "Drivers are now very young and take on huge responsibilities."

For Nasr and Ericsson, the media spotlight may not be as bright as at the front of the grid, but the money brought to Sauber by their personal sponsors means they are central to the very survival of the team.

"Suddenly," said Ceccarelli, "they realise not only their future but that of the team is in their hands. And, I repeat, they are very young."

Better in all areas, Ericsson said he is happy to be ahead of his teammate for now.

"I am in front now but I cannot relax," he insisted. "He's trying, of course, to come back and beat me, so I have to keep working hard."

(GMM)