Polish Formula One driver Robert Kubica will announce on Thursday his decision to leave the Williams team at the end of the season, private radio RMF and sports daily Przeglad Sportowy reported.
Kubica is one of five drivers scheduled to appear at a news conference organised by the governing FIA at the Singapore Grand Prix scheduled for 2030 local time (1230 GMT).
The Polish media reports, without naming their sources, said Kubica`s sponsor, Polish oil refiner PKN Orlen, will also end its deal with Williams.
A Williams spokesman had no immediate comment while PKN Orlen declined to comment.
Williams are last in the championship with just one point, scored by Kubica.
The 34-year-old Pole, a race winner with now-defunct BMW-Sauber in Canada in 2008, made an astonishing comeback to Formula One this season after a near-fatal rally accident in 2011 left him with a partially severed right forearm.
He remains the only Polish driver to have raced in the Formula One world championship.