Williams have the spares they need for Sunday's Bahrain Grand Prix, deputy principal Claire Williams said on Friday in response to concerns raised by the Formula One team's Polish driver Robert Kubica.

Kubica told reporters at the Sakhir circuit on Thursday that the struggling former world champions were short of spare parts and would have to play safe on track to avoid any damage to the cars.

Williams were late to finish their 2019 car and missed two days of pre-season testing. They were also slowest by some margin in the Australian season-opener two weeks ago.

Kubica claimed he would have to play it safe on track

"Inevitably we've got a little bit of a backlog from not having got the car out when we needed to in testing but everyone's worked really hard at the factory to make sure we've got the spares we need," Williams told Sky Sports television.

"We've got spares for all the parts that we need. We've just got to make sure that the drivers don't do anything on track to jeopardise that," she added.

"I think a lot of teams at this time of year anyway are in a similar kind of position, clearly we didn't help ourselves but it's not anything that I'm overly concerned about."

Kubica and British rookie team mate George Russell, last year's Formula Two champion, were slowest in Friday's first free practice in Bahrain, some 3.8 seconds of the pace set by Ferrari's Charles Leclerc.

Russell said in Australia that the car had a 'fundamental problem' that would take months to fix. Kubica told reporters on Thursday that it was not an easy situation.

"We will be limited with spare parts and everything," he said. "You cannot go over the kerbs, or you go over the kerbs but the risk is that the car will fall apart and then you have no parts to fit them."

Patrick Head during his last spell with Williams in 2011

Meanwhile, Williams co-founder Patrick Head has returned to the team as a consultant after they started the season with an uncompetitive car that even their own drivers say is fundamentally flawed.

The 72-year-old Briton, who founded the team with Frank Williams in 1976 and oversaw a string of title-winning cars in the 1980s and 90s, stepped away in 2011 but retains a nine percent shareholding.

Williams finished last overall in 2018 and technical head Paddy Lowe, the man who had ultimate responsibility for this year's car, left on a 'leave of absence' before the season started.

The British team said in a statement from Bahrain that Head was "currently offering some support to our engineering team on a short-term consultancy basis."