George Russell compared the Mercedes W14 to "a lame horse", following on from previous criticism of the car by his team-mate Lewis Hamilton.
Last month, Hamilton called out his team in public, accusing them of not listening to his input on the design of the car. He later said he probably should have used different words, but is still "miserable" about working with a car with which he says he has no connection.
He later complained about his seating position in the W14, which he feels is too far forward. Responding to that particular problem, team principal Toto Wolff said it was something they would be working on as he sent a message to his staff.
