Felipe Massa and Robert Kubica's father have both suggested the power of financial backing is swaying Williams towards choosing Sergey Sirotkin to partner Lance Stroll for 2018.

The Russian has emerged as the favourite to replace Massa, who retired from Formula 1 at the end of last season, that comes after a strong showing at the post-season test in Abu Dhabi and the promise of around EUR15m in sponsorship.

If the F2 driver was to get the nod, it would be at the expense of Kubica who is looking to make what would be a welcome comeback to the grid seven years after his first stint was cut short by the terrible injuries he sustained in a rally crash in early 2011.

For the Brazilian, whoever Williams choose it will be for the money after effectively counting himself out of the seat by announcing his decision prior to his home race in Sao Paulo.

"The path of the team is financial, including Kubica, so it does not surprise me," he claimed of the Sirotkin speculation. "But I don't know what will happen, I'm not following the team now. My thoughts are in other things and what I'm doing from now, and it's not F1 anymore."

It was reported by Russian media that the 23-year-old could be announced as soon as today (Friday) but the Grove-based team has claimed no decision has yet been made with Kubica's father Artur claiming his son's management team are still pushing hard.

"We're still fighting to get Robert into Williams," he told Poland's Sportowe Fakty. "We hope that it is a good decision for us and if it is not made before Christmas, it means that at least the people at Williams are taking time to think.

"We are taking steps to convince them to believe in Robert."

He admits, however, a reported EUR7m difference between the backing the 32-year-old compared to Sirotkin could be crucial.

"Of course it is about what the driver will bring to the team. Sometimes, skills, experience and the potential of the driver are decisive, at others only the money counts," admitted Kubica senior