Mercedes race engineer Pete Bonnington, the man who guides Lewis Hamilton on Grand Prix weekends, will miss the Mexican and US races to undergo a personal medical procedure in the UK.
Bonninton - or "Bono" - is the instantly recognizable voice on Hamilton's radio and the valuable strategist who has helped the Briton secure his four titles with Mercedes.
"Bono is not in Mexico this weekend and will not be in Austin either owing to a medical procedure back in the UK," said a spokesman for Mercedes.
"Lewis will be engineered by Marcus Dudley, usually his performance engineer standing to Bono's right in the garage.
"Performance engineer for the two weekends will be Dom Riefstahl, who usually runs our race support operations in Brackley."
Hamilton has a reasonable shot of clinching his sixth world title in Mexico City, but if the 34-year-old secures the crown on Sunday it will be the first time Bonnington won't be present for the coronation.
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