By Alan Baldwin
MEXICO CITY (Reuters) - Lewis Hamilton will be without the reassuring voice of long-term race engineer Peter Bonnington as the Mercedes driver seeks to clinch his sixth Formula One world championship in Mexico or Texas.
The team said on Friday that 'Bono', familiar to television viewers worldwide for his radio messages to Hamilton, was missing the next two races due to "a personal medical procedure".
Bonnington has performed a key role throughout Hamilton's seven years at Mercedes and can be heard telling the Briton to pull out all the stops with the catchphrase 'OK Lewis, it's Hammertime."
"I've had Bono by my side my whole time here at this team, and you can hear our rapport when we're in a race," the driver said last year.
"Bono is fantastic at managing, because there is a lot of commotion going on on the wall and everyone is saying tell him this or tell him that, and Bono knows what to filter," Hamilton added in Austria in June.
"He is the best filter. He always comes across calm and cool and collected."
Bonnington's role will be taken by performance engineer Marcus Dudley, with Dom Riefstahl stepping into Dudley's shoes.
Hamilton can wrap up the title, becoming only the second six-times world champion in Formula One history after Michael Schumacher, in Mexico if he scores 14 points more than Finnish team mate Valtteri Bottas.
If that looks something of a long-shot, with Hamilton having to be on the podium at the very least, then the following weekend in Texas should be the clincher barring any major drama at the Autodromo Hermanos Rodriguez on Sunday.
Bonnington is expected to be back for Brazil and the finale in Abu Dhabi.
Hamilton, who has only once this season scored 14 points more than Bottas in a race, told reporters he was not fussed about where he won the championship.
"I anticipate that it will be a difficult weekend. Valtteri has been strong all year and obviously won the last race, so I expect him to be strong this weekend too," he said.
"It doesn't matter where it's done as long as you get it done, and that's what I'm trying to do.
"But I'm fully aware that there are still plenty of points on the table and I've got to deliver over these next four races."
(Reporting by Alan Baldwin; Editing by Hugh Lawson)