Jul.15 (GMM) Team boss Mario Theissen is still giving no hints about the identity of BMW-Sauber's driver lineup for the 2009 season.

It is no secret the Hinwil based outfit is keen to retain on-form Polish racer Robert Kubica, but his experienced teammate Nick Heidfeld has had a disappointing run of results this season in the sister car.

It is understood 31-year-old Heidfeld, a German, has a contract for next year, and his second place at Silverstone recently suggested he is now getting to grips with his problems with the F1.08 single seater.

But in an interview with Auto Motor und Sport, Theissen is giving nothing away about BMW-Sauber's plans for 2009.

"We will announce our driver pairing for 2009 between the (August) summer break and the end of the season. So for the moment nothing has changed," he added.

When asked specifically about Heidfeld's improving form, Theissen continued: "A team that wants to play a role in the world championship needs two strong drivers.

"However, even the best driver is not a robot. He can only deliver maximum results if the equipment, the environment and everything else is right.

"At Silverstone Nick gave a convincing performance; strong in qualifying, fast in the race, with spectacular overtaking manoeuvres and very good vehicle control in very difficult conditions," Theissen said.

"For me this is the fruitful result of the past weeks of intensive work. I am convinced that, in the second half of the season, we will see a strong Nick Heidfeld," he added.