(FILES) A photo taken on April 21, 2012 shows Mercedes driver Michael Schumacher from Germany during the third practice session at the Bahrain international circuit in Manama ahead of the Bahrain Formula One Grand Prix. Schumacher will leave Mercedes at the end of the Formula One season, and being replaced by British driver Lewis Hamilton Mercedes confirmed on September 28, 2012. AFP PHOTO / KARIM JAAFAR

Mercedes boss Dieter Zetsche has insisted Michael Schmacher's disappointing return to Formula One has been due to their underperforming car and not the driver.

Schumacher, 43, returned to Formula One in 2010 after a four-year hiatus, but the seven-times world champion has failed to make an impact on the world Drivers' championships.

Zetsche, the head of Mercedes-Benz, told Wednesday's edition of German daily Bild: “We have not been able to provide both drivers (Schumacher and team mate Nico Rosberg) in the past three years with a car that was able to win the majority of races.”

“With the engine we were competitive, but not with the car. And it would be completely wrong to reproach either Nico Rosberg or Michael Schumacher.”

Last week, Mercedes announced it would not be extending Schumacher's contract.

He will leave Mercedes at the end of the season, with Britain's Lewis Hamilton set to join the German team.

But Zetsche insisted Schumacher's age wasn’t a factor, citing Argentina's Juan-Manuel Fangio, who was a world champion at the age of 46, during the 1950s.

The German admitted that “given the name of Michael Schumacher, expectations were probably too high”.

“But I called Michael on the day the decision was announced to speak with him. It was a very good discussion,” Zetsche added without elaborating.

Schumacher won the last of his world titles in 2004 with Ferrari and finished eighth last season with Mercedes fourth in the Constructors' championships.

Having made his Formula One debut in 1991, he has raced in more than 300 Grand Prix, winning 91 of them, but none since his return. - AFP