Robert Kubica is adamant his performances are being "overshadowed" by the pace of Williams this season.

The Pole's highly-applauded Formula 1 comeback after eight years has been subdued by the difficulties of the British team, with their car well off the pace of the rest at the back of the grid.

However, his pace compared to teammate George Russell has also been disappointing, leading to questions over whether he should have returned.

"It's not easy to see the progress, there are many positive things, but they are overshadowed by the overall performance," he told Motorsport-Total.

"My pace and driving style is better than the results show."

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The problem facing Kubica and Russell is the likelihood of Williams closing the gap simply to the midfield appears unlikely, based on the rate of progress they have made so far.

Which means the pair may be left to simply battle each other for the rest of 2019.

"That is the situation now. It would be nice if we didn't struggle with even more problems that make driving even more difficult for us," Kubica added.

"We have to be on top of those problems and come up with solutions, but we haven't succeeded so far. First of all, we have to understand where the problems lie."