Former world champion Jacques Villeneuve has left BMW Sauber with immediate effect in a move which could bring his Formula One career to an end.
This is really disappointing as I was looking forward to working with BMW in the long term
The Canadian's contract was due to expire at the end of the season but has now been terminated by mutual consent.
The 35-year-old did not race in the Hungarian Grand Prix, with Polish test driver Robert Kubica taking his place.
Villeneuve won the world title in 1997 with Williams but says he has received no firm offers for next season.
Villeneuve, who raced in 163 grands prix, blamed the split on the lack of assurances about his short-term future with BMW Sauber.
But reports suggested his absence was more a case of the team looking to the future with Kubica.
The Pole, 21, finished in seventh place in Hungary before being disqualified when his car was found to be underweight.
He had been handed the drive at the Hungaroring because Villeneuve was still suffering the after-effects of a crash in Germany.
"Last week, the team informed us of its decision to review its options for next year, including assessing Robert Kubica in a race environment, without offering me any assurance about my race seat beyond Hungary," said Villeneuve.
Villeneuve, 35, walks away after his crash at Hockenheim
"Therefore, the team and I agreed to part ways with immediate effect.
"This is really disappointing as I was looking forward to working with BMW in the long term - going into next season capitalising on our common experiences.
"I will now have more time to concentrate on future projects.
"Finally, I would like to thank the team, especially my engineers and the team's sponsors with whom I have had real pleasure working with in the last year."
BMW motorsport director Mario Theissen said the decision had been taken with the best interests of the team in mind.
"Jacques has performed well for us this year, scoring the team's first Grand Prix points in Malaysia," said Theissen.
"He has made a significant contribution to developing the newly formed BMW Sauber F1 team and the performance of the car
It's difficult for Jacques to maintain his commitment in circumstances of uncertainty
BMW motorsport director
"However, after Jacques' accident in the Hockenheim race, the team decided to review its options for next year, including assessing Robert Kubica in a race environment.
"Our decision to look towards evaluating our driver line-up has naturally impacted Jacques' position for the remainder of the season.
"We fully understand it is difficult for Jacques to maintain his natural level of commitment in circumstances of uncertainty.
"We respect his position and wish him well for the future."
Villeneuve has already complained about the lack of offers he had received in F1 and now looks likely to pursue other forms of racing, with one-off races like Le Mans in the frame.
He won 11 grands prix when he claimed the title with Williams but left to join the new BAR team, for whom he struggled.
He raced for Renault in 2004 before joining Sauber on a two-year deal in 2005.