Robert Kubica's brief return to Formula One will conclude at the end of the year after the Polish driver announced he is leaving Williams.

Kubica completed one of sport's finest comebacks by landing a seat on the F1 grid eight years after he was nearly killed in a rally crash.

But the 34-year-old has struggled for form on his return to action, propping up the field in an under-competitive Williams.

"I have taken the decision that I will not continue with Williams," said Kubica ahead of this weekend's Singapore Grand Prix.

"I feel that the time is right to move on to the next chapter of my career."

Kubica said he hoped to remain in the sport, but appears to have next to no chance of securing a seat for 2020.

Before his rally accident, Kubica was regarded as one of the finest drivers of his generation.

One month before the start of the 2011 season, Kubica was left fighting for his life after he lost control of his car while rallying in Italy. He partially severed his right arm and sustained multiple fractures.

Kubica worked tirelessly to return to F1, landing a reserve drive with Williams in 2018 before securing a full-time drive this year. He has scored just once, a 10th place finish in Germany.