London - Williams' head of performance engineering Rob Smedley will leave the Formula One team at the end of a dismal season for the former world championship winning team, which is struggling to score points.
The 44-year-old joined the British team from Ferrari in 2014 with now-departed Brazilian driver Felipe Massa, with whom he had a very close working relationship as his race engineer.
The Briton became a familiar voice to fans for his radio messages to Massa at Ferrari, including one at the 2010 German Grand Prix in which he relayed a team order for the Brazilian to move over for Fernando Alonso while leading.
"OK, so Fernando is faster than you. Can you confirm you understood that message?" he said.
Williams quoted Smedley in a statement as saying that after 20 years in Formula One "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," he added.
Williams is last in the constructors' standings with a meagre seven points from 19 races so far this season despite having the same engines as champion Mercedes. Its closest rival, ninth placed Toro Rosso, has scored 33.
The once-dominant team has not won a race since 2012 and its form has gone through peaks and troughs in recent years, from ninth in 2013 to third in 2014 and 2015 and then fifth in the last two years.
Deputy principal Claire Williams said the team, whose only confirmed driver for 2019 is Mercedes-backed British rookie George Russell, would miss Smedley but respected his decision.
"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," she said.
Williams' chief designer Ed Wood left for personal reasons in May while head of aerodynamics Dirk de Beer left in the same month.