But Kubica's co-manager, 2016 world champion Nico Rosberg, told Auto Motor und Sport that the test and reserve role the 32-year-old has secured is still positive.
"Robert will be able to do many kilometres," Rosberg said.
"For him, it's a mega contract and definitely a step in the right direction."
Kubica had put together an $8 million sponsorship purse for the race seat, but Auto Motor und Sport claims that he will actually be paid by Williams this year.
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