Michael Schumacher has hinted that his car has not always been on the same performance level as team-mate Nico Rosberg's Mercedes this season.

The seven-time world champion has endured a torrid season on his return to Formula One racing and has been consistently out-qualified and out-raced by the younger Rosberg.

And although Schumacher managed one of his better outings of the season with a sixth place finish in the Japanese Grand Prix, he indicated that there have been more problems with his car than with Rosberg's.

"The car worked great this time," Schumacher told German television channel RTL. "Unfortunately, I cannot say it has been that way at all the races.

"There have often been problems, especially on my car, in terms of the consistency, that were not always noticed from the outside. You only saw that I was slower. Both cars have not always been the same."

Mercedes' Norbert Haug did not disagree with Schumacher's claims.

"I cannot disagree with Michael. As far as the car is concerned, he is right," Haug told Bild newspaper.