Robert Kubica's hopes of a Formula 1 return are set to be dashed with Williams now likely to sign Renault reserve Sergey Sirotkin for 2018, according to reports.

Both men drove for the Grove-based team during the post-season test in Abu Dhabi and though many overlooked the Russian's presence, it appears his pace at Yas Marina, which was believed to be quicker than the Pole's, allied to around $15m in backing has now made him the favourite to replace the retired Felipe Massa.

At only 22, appointing Sirotkin would mean Williams did not meet what many thought to be a mandatory requirement of their partnership with title sponsor Martini of having at least one driver over the age of 25 for promotional purposes, but that now doesn't appear to be an issue.

To miss out, however, would be a major blow for Kubica after completing a number of F1 tests this year, firstly with the Renault team in the summer and more recently with Williams. The former Grand Prix winner also enlisted the help of 2016 world champion Nico Rosberg onto his management team.

His pace during his first outings in an F1 car since his near-fatal rally crash in 2011 has been impressive but lingering concerns appear to remain along with the attractive proposition but forward by Sirotkin.

One report still suggests Kubica could be in the frame if the F2 driver's financial backing deal was to collapse but another claims Daniil Kvyat would be an alternative as he also has strong backers despite leaving the Red Bull program this year.