Williams has confirmed vehicle performance chief Rob Smedley will leave the team at the end of 2018.
Smedley joined Williams in 2014 from Ferrari and helped guide the team to two consecutive third-placed finishes in the contructors' championship. The team has been unable to sustain that form, however, and has slumped in recent seasosn -- this year, its sits bottom of the same table with just seven points to its name.
The Englishman is uncertain what his next move will be.
"I have thoroughly enjoyed my time at Williams," Smedley said. "The team has been through great change since I joined in 2014 and it has been a pleasure to have played a part in that.
"Williams is a very special team within the F1 community and I'm certain that with all the talent that we have here they will go on and do better things. The team will always remain close to my heart. After 20 years in Formula 1, however, I feel it's the right time to reflect on things and evaluate what the next move is.
"I'm thoroughly looking forward to spending more time with my family before deciding on future opportunities."
Deputy team principal Claire Williams said: "It has been a pleasure having Rob in our team for the last four years and we will miss him both personally and professionally. He agreed to join us at a time when our performance was low, and we are grateful that he saw the potential for us to turn things around at that time.
"During his time with us, he has made a significant contribution to the team through his role, but he's also been just a great person to have at Grove, inspiring many with his enthusiasm and passion for Formula One.
"Rob's been in the sport a long time, so we totally understand and respect his decision to take some well-deserved time out to spend with his wife and boys. We wish him all the best and thank him wholeheartedly for the time, passion and fighting spirit he's given to Williams."
Smedley's career in F1 started with Jordan, before he moved to Ferrari in 2004. He came to prominence as Felipe Massa's outspoken race engineer during that stint and was the man who gave him the now-infamous coded message "Fernando, is faster than you" at the 2010 German Grand Prix, when Ferrari controversially told the Brazilian to move across for Fernando Alonso to inherit the win. Smedley made the switch to Williams when the Brazilian moved there for the 2014 season.
His departure continues a shake-up at Williams, who company with former head of aerodynamics Dirk de Beer and chief designer Ed Wood in May.