Williams could finally get their troubled new Formula One car on track on Wednesday, five days later than planned and well behind rivals already pounding out laps in testing.
The former champions, who finished last overall in 2018 and have shed a number of sponsors, had planned to debut the car last Saturday for a limited mileage filming session at Barcelona's Circuit de Catalunya.
That deadline slipped because the FW42 was not ready and Williams were then the only team unable to make the start of official pre-season testing on Monday.
A Williams spokeswoman said the car was now expected to arrive at the circuit between 0300-0400 GMT on Wednesday but was unlikely to run in the morning session that starts at 0800 GMT.
"Obviously there will still be a fair amount to do but we will be working as fast as we can," she added.
The first pre-season test ends on Thursday with a further four days next week before the teams head out for the opening race in Australia on March 17.
The lack of testing time is a big setback for a team hoping to clamber back from one of their worst ever seasons and pinning their hopes on coming up with a much better car than the woeful one produced last year.
Williams, who took nine constructor's titles and seven driver's crowns during their glory years between 1980 and 1997, scored only seven points from 21 races last year.
The inability to produce the car on time has raised questions about the future of technical head Paddy Lowe, who joined in 2017 from champions Mercedes and is the man ultimately responsible for delivering it.
The Formula One website reported fears that the new car, based on data simulations, could also be almost two seconds slower than its closest rival when it does hit the track.
Williams have not given details of why deadlines were missed, fuelling speculation that there could be a serious problem with the design that has needed fixing.
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