Kokubu has been a mainstay at the Japanese manufacturer for over three decades, having joined Honda in 1986, working on both its MotoGP project and briefly in Formula 1.
He did not travel to India last week and is also not present at Motegi for the Japanese Grand Prix, and will most likely be followed in a few months by Tetsuhiro Kuwata, who has a more administrative than technical role.
Kokubu's time with Honda in MotoGP is especially significant, having been responsible for the chassis of the RC211V raced by the marque in 2003 right at the beginning of the four-stroke era of the premier class.
With that chassis, Honda won two world championships with Valentino Rossi and a third with Nicky Hayden before the RC212V was introduced for 2007 at the start of the 800cc era.
In 2008, Kokubu was appointed as project leader of the RC212V and became technical director in 2012, before taking on the role as general manager of Honda's technical and development division in 2016.
Source: Autosport