Michael Schumacher expects the Mercedes GP car to be "competitive" this season but isn't sure if the team can win the Formula One championship.
Schumacher will be aiming for an eighth Formula One title.
Schumacher was pleased with his first full day of driving a competitive F1 car on Wednesday, saying it was "running very smoothly, very nice, I'm looking very positive into the season."
But he didn't sound bowled over in his return after a three-year retirement.
"We will be competitive, but whether it's right away a winning car or not that's another story," Schumacher said. "I wouldn't expect to be winning right from the beginning, it wasn't something I was aiming for and expecting to be the case. But we need to be strong enough in the development."
The 41-year-old German drove 82 laps to close the preseason's first testing session before a hydraulic leak forced him off with the third-fastest lap time. It was nearly one second slower than pace-setter Fernando Alonso of Ferrari.
Schumacher said improvements are needed because he considers his former Ferrari team a potential front-runner.
"We need to be there, we need to take good points at the beginning," Schumacher said.
Schumacher and most of the F1 teams will head to the next test session from Feb. 10-13 in Jerez, Spain.
"The main focus now is to look at the reliability, to do as many laps as you can and not worry too much for the lap times," Schumacher said. "Yes, you look at (the lap times) but you need to pinpoint and focus on main, important (things)."
He did find it easier than expected to return as he pairs again with team principal Ross Brawn, who was instrumental in each of his seven previous championships. Brawn GP won both drivers and constructors' titles last season before being bought by Mercedes.
"Much easier than I expected it," Schumacher said of adapting to an F1 car. "I thought it needed more time, but it went pretty quickly." AP