Lewis Hamilton will look to secure his sixth world title at the Mexican and United States Grads Prix without the trusted voice in his ear of race engineer Peter Bonnington.
Bonnington has been Hamilton's race engineer since his move from McLaren to the Silver Arrows in 2013, helping him to four world titles in the past five seasons.
He is closing in on a fifth championship with Mercedes and has his first chance to do so in Mexico City this weekend.
However, Bonnington will not be by his side as he undergoes a medical procedure, which will also see him miss the race at the Circuit of the Americas in a week's time.
Hamilton's performance engineer Marcus Dudley will fill Bonnington's shoes, with Dom Riefstah – who heads up Mercedes' support efforts at their headquarters during races – heading o Mexico and the US to take Dudley's place.