Tim Goss, the single-seater technical director at the FIA, has bid adieu to his role, marking the departure of the third high-profile figure in the past month.
The FIA has appointed Tim Malyon, who has served as the safety director since 2021, to step into Nielsen's shoes.
Goss's departure leaves a notable void in the single-seater technical director role, with the organisation yet to announce a successor.
Tombazis: Goss going in new direction
"We are disappointed to lose a person of Tim's calibre from the organisation," Nikolas Tombazis said as per BBC Sport.
"Tim has played a major part in the technical department and has always operated to the highest level.
"We understand that his career is taking a new direction going forward and we support and respect his desire to pursue another path."
An FIA statement quoted Goss saying that the FIA are on a 'firm footing' heading into the 2026 regulation changes.
"I believe the organisation is on a firm footing in terms of technical expertise for the tasks which lie ahead - particularly the introduction of the 2026 regulations," he said.