Robert Kubica will leave former champions Williams at the end of the season, a move likely to bring the curtain down on the Polish driver's extraordinary F1 racing comeback following a rally crash eight years ago.

The 34-year-old made his race return this season after suffering near-fatal injuries, including a partially severed right arm, in a minor rally in Italy on the eve of the 2011 season.

"In order to evaluate other opportunities I have taken the decision that I will not continue more with Williams after this year," he told reporters at a Singapore Grand Prix news conference.

"It took... a lot of time to recover and come back to the sport. I said this year will be a goal to remain in F1... but not at every cost.

"I have to first of all do what will bring me back a bit of joy of racing. This season has been very tough from a performance point of view, but it has been also very demanding. Being back in F1 after a long time is not easy."

Williams are last in the championship after 14 races with an uncompetitive car and just one point scored by Kubica in Germany after drivers ahead of him were demoted by penalties.

Kubica, a race winner with now-defunct BMW-Sauber in Canada in 2008 and once seen as a potential champion, remains the only Polish driver to have competed in the F1 championship.

Mercedes' five-time world champion Lewis Hamilton, a boyhood rival in karting, hailed Kubica's strength and determination.

"Not a lot of people can come through those circumstances and come back, make it back into the sport and deliver against others who don't have the same situation that he's been in. I think it's been great to have him back," Hamilton said.

"I understand his position and I don't know what's given him the reason to make the decision but I hope there's a position for him next year."

French driver Romain Grosjean said Kubica had been an inspiration. "In motorsport he is an example, but also in life generally, to come back to the highest level and... fight the way he fought back is very impressive."