The former champions finished last overall in 2018 and started the new season badly, with their car late to testing and then significantly slower than the rest despite having a winning Mercedes engine.
Williams qualified at the back of the grid in this month's Australian season-opener.
"It is not an easy situation also from a drivers' point of view because we will be limited with spare parts and everything," Kubica told reporters at the Sakhir circuit ahead of Sunday's second race of the year.
"It is putting the driver in a difficult position," added the Pole, whose car's performance was compromised in Melbourne when he damaged his car's floor in practise.
"Tomorrow the situation is like it is. 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."
Kubica, who returned to Formula One this season eight years after a near-fatal rally crash partially severed his right arm, recognised the British-based team were doing their best.
"But on the other hand I think in a perfect world you would have fresher parts starting a weekend and having some spare parts in a good state," he added.
Team mate George Russell told reporters in Australia that Williams had identified a 'fundamental issue' with the car but it would take time to fix.
In Bahrain, the 21-year-old Briton said being at the back of the grid in Melbourne had brought other drawbacks because he had been unable to see the starting lights due to the taller rear wings the cars are sporting this year.
“I pulled up onto the grid, looked up and realised I couldn't see anything," said the 2018 Formula Two champion.
"I was looking all around and I ended up seeing the lights through the reflection of the Paddock Club (hospitality) windows.
"At the back of the grid (in Melbourne) the track dips down very slightly so the rear wing of the car ahead would seem higher," he said. "I'm not sure if it'll be an issue at all tracks, but we'll find out on Sunday..."
(Editing by Alan Baldwin and Toby Davis)
Share
