Williams technical chief Paddy Lowe has taken a "leave of absence" from the team on the eve of the 2019 F1 season.
The news comes a fortnight after Williams missed the first two days of winter testing amid delays in the build of their new FW42 car.
Williams said in a statement that "Paddy is taking a leave of absence from the business for personal reasons."
The Grove-based team did not elaborate on the short statement and whether their chief technical officer will return.
The Australian GP takes place on March 15-17.
Lowe's Williams stint at an end?
Lowe's future had already been the subject of growing speculation since news of Williams' car delays emerged.
Claire Williams, the outfit's deputy team boss, admitted the late start was "embarrassing" for the former world champions ahead of a new season in which they are targeting progress back up the grid.
Lowe joined the team at the start of 2017 from world champions Mercedes but the outfit finished bottom of last year's Constructors' Championship for the first time in their illustrious history.
Asked directly about Lowe's position at the first Barcelona test, Williams said: "I've been reading a lot of speculation in the media recently about Paddy's position. Right now all I'm focused on, all the team should be focused on, is the car and making sure the car is in the right place."
Lowe, who started his career at Williams in the late 1980s, said at last week's second test that he believed he retained the support of the team's senior management.
Asked by Sky Sports News if he remained confident he was the right man to take Williams forward, Lowe replied: "Absolutely, but I won't do it single handed.
"This is a team effort and we've certainly got some very strong people in the team. There's a great job to be done and a great job of work and we certainly don't underestimate the challenge there. Given time, we can turn this team back to its days of former glory."
Lowe added to reporters: "Quite often the habit is to change people when things don't work. But what I've also observed in Formula 1 is that the stronger teams are the ones that don't do that. Every problem within a team is an opportunity to learn... I'm not aware of any different view."
Where will Williams be in Melbourne?
Although Williams quickly racked up lots of mileage across their five-and-a-half days in action at Barcelona with the FW42, the team are expected to be at the back of the 10-team field for at least the opening race.
Writing in a detailed analysis feature of the likely Melbourne pecking order, Sky F1 pundit Karun Chandhok said: "Williams arrived at the party late and unfortunately for them, unlike the Brawn in 2009 or the McLaren MP4/4 in 1988, they haven't shown signs of springing a surprise.
"The car does look like it's lacking grip and downforce out on track meaning that highly-rated rookie George Russell and F1's most popular returnee Robert Kubica could be in for a battle amongst themselves initially."