Pole Kubica is looking to return to F1 after a seven-season absence due to a permanent arm injury. He has tested for Renault this year and is now in the running to replace Felipe Massa at Williams in 2018.
But Germany's Auto Motor und Sport said the 32-year-old's management, including the reigning world champion Rosberg, is not pushing for the Gasly seat.
Reportedly, one of the reasons is that when Kubica does return, he would have to give back a lifetime insurance payout he received for being permanently unable to race in F1 -- even if that comeback is for one race only.
And Rosberg said Toro Rosso's one-race opportunity would be too great a risk for Kubica.
"If you are thrown into deep water in a strange car without a test, you can only lose," said the German. "It is better to keep going for the Williams opportunity."
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