Williams have suffered another major setback after it was confirmed they will now miss the second day of winter testing.

With their car not ready for activity, the British team were the only outfit absent from the first meaningful action of pre-season at Barcelona's Circuit de Catalunya on Monday.

And deputy team principal, Claire Williams has revealed that Williams – which finished rooted to the foot of the constructors' championship last year – will not be on track until at least day three of this week's four-day first test.

"It is looking more likely than not that we will now not be in a position to run on track until Wednesday at the earliest," said Williams.

"This is obviously extremely disappointing, but it is unfortunately the situation we are in."

British rookie George Russell, who celebrated his 21st birthday last week, and the returning Robert Kubica were already playing catch-up for a team bidding to bounce back from last season's miserable campaign.

Following this week's test, there will be just four further days of running before the new season starts in Melbourne on March 17.

Out on track, Ferrari driver Sebastian Vettel was the fastest out of the blocks on Monday.

The four-time world champion posted a time 1.7 seconds quicker than the best lap set on the opening day of testing last year.

Despite an early spin, Vettel had completed 72 laps, the equivalent of more than a race distance, by the lunch break.

Racing Point's Sergio Perez was second on the time sheets ahead of Mercedes driver Valtteri Bottas.

Five-time world champion Lewis Hamilton will take over testing duties from team-mate Bottas on Monday afternoon.