Vasselon, 60, has been succeeded on a temporary basis by David Floury as the technical chief of the Cologne-based organisation that masterminds Toyota's World Endurance Championship programme, develops the engines for its World Rally Championship GR Yaris Rally 1 and builds the GR Supra GT4 customer racer.
The move announced on Monday was described in a short statement from TGR-E as part of a drive "to develop the next generation of company leadership as part of its commitment to continuous improvement and making ever-better motorsport-bred cars".
Vasselon will remain with TGR-E, which was formerly known as Toyota Motorsport GmbH (TMG), although his role in "day-to-day operations is temporarily paused", according to the statement.
It went on to say that it is expected that he will "resume an active role soon, contributing his knowledge and experience to enhance TRG's strategic approach to global motorsport".
Vasselon joined Toyota in 2005 from Michelin, where he managed its involvement in Formula 1.
The Frenchman was initially head of chassis research and development before his promotion to the role of technical director in 2006 in place of Mike Gascoyne.
After Toyota's withdrawal from F1 at the end of the 2009 season, he oversaw its entry into the top class of the WEC in 2012 and its five Le Mans 24 Hours victories and five drivers' and manufacturers' championship doubles.
Vasselon has been linked to a role in the programme designed to put a prototype powered by a hydrogen combustion engine on the grid in the WEC in 2027.
The Japanese manufacturer confirmed its plans with the unveiling of the GR H2 Racing Concept on the eve of Le Man last year.
Floury steps up to become acting technical director of TGR-E after a long involvement with the Toyota WEC programme.
He was chief race engineer from the beginning of the WEC project as part of the link-up with the French ORECA team, which provided operational support for the Toyota WEC squad.
The Frenchman dovetailed his Toyota duties with his role as technical director of ORECA until joining the staff at Cologne in 2021.
The reshuffle was described by TGR-E as the "first step in an updated management organisation".
The process has been implemented by TGR-E president Misato Hirai, managing director Rob Leupen and Kazuki Nakajima, who became vice chairman on his retirement from the cockpit at the end of 2022.
John Litjens and Norio Aoki, respectively project leaders on the WEC chassis and WRC engine programmes, retain their roles and will report to Floury.
