Former Renault Team Principal Flavio Briatore says he is "very sorry" after being told Robert Kubica's attempted comeback to Formula 1 with Williams will end in failure.

The Pole has been working towards what was once considered an impossible return to the grid, seven years after a horrific rally crash left him with severe injuries. Limitations continue in his right arm but that didn't stop the 32-year-old from initially with Renault before focusing on the seat formerly held by Felipe Massa.

Though yet to be confirmed, F2 driver Sergey Sirotkin is now expected to line-up alongside Lance Stroll in 2018 and Briatore claims the deal is already done.

"I have talked to Nico Rosberg [Kubica's co-manager] several times and know that everything has been tried, but the Russian has an enormous budget," he told Austria's Speed Week. "We're talking about 20 million and Kubica could muster between 7-10 million.

"I'm very sorry that Kubica did not manage to convince Williams."

While former world champion Jacques Villeneuve admits he isn't surprised money has been the most influential factor, the Italian laid some of the blame at the feet of F1 bosses who will now miss out on the publicity and interest Kubica's attempted comeback brought.

"If Robert had returned to F1, it would have been a major success for the sport," he said. "I find it very strange that the F1 leadership did not lend him a helping hand."