Williams will miss the start of 2019 Formula 1 pre-season testing at Barcelona on Monday because the build of its car is still running late.
The team had already been forced to scrap plans for a weekend shakedown, and now it has announced it will be a day late in starting official running.
Claire Williams, deputy team principal, said: "Unfortunately, we have had to delay the start of our pre-season Barcelona test to Tuesday morning.
"We have had an incredibly busy winter at Grove getting the FW42 prepared for the season ahead and, despite everyone's best efforts, we need some more time before it will be ready to run."
Williams is coming off the back of a disappointing 2018 campaign where its performance fell far short of expectations.
It finished last in the constructors' championship and has made changes to its infrastructure in a bid to try to turn things around.
"Our absolute priority is to always ensure we bring a car to the track that is the best that it can be and sometimes that takes longer than you'd anticipate or like. It's clearly not ideal, but equally it's not the end of the world," added Williams.
"We will obviously have our work cut out to recover the time lost but we still have seven days of testing left and we will be maximising that time to prepare the car for the first race."
The team goes into 2019 with an all-new driver line-up as George Russell and F1 returnee Robert Kubica replace Sergey Sirotkin and Racing Point-bound Lance Stroll, and a new title sponsor in ROKiT.