Robert Kubica's sponsor has asked Williams to provide an explanation for the Polish driver's retirement from the Russian Grand Prix.
Kubica, who will leave the team at the conclusion of the 2019 season, was brought into the pits to retire the car one lap after teammate George Russell crashed during a Virtual Safety Car period. Williams put that incident down to an unspecified car issue and said the decision to retire Kubica's car was precautionary.
After the race chief race engineer Dave Robson said: "We opted to retire Robert soon afterwards in order to conserve parts ahead of the intense flyaway races which end the season.