Sergey Sirotkin has praised his time with Williams and admits he feels "sorry" about their recent woes.

On Wednesday, the Russian confirmed he would return to Renault in 2019 as reserve driver, a position he held before joining the British team last season.

However, speaking in Barcelona, unsurprisingly he was asked about the state of Williams, who missed over half of last week's first test due to delays with their car.

"We all know [Williams] is in a very difficult position, but at the same time, I have so many great friends there, so many great people," Sirotkin commented.

"I know that we only spent a season together but it's a very long year and we spent so many days together at the factory, together at race tracks, all along working together in such a difficult situation so it really feels like I was there forever.

"I really feel sorry for them [in their current situation]," he added. "I know how much work we altogether put into development and I feel really sorry because of certain difficulties they will not see that as a result in terms of performance.

"I know the people there and what they deserve, so I just want to wish them all the best and really hope that they will get what they really deserve."

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Sirotkin, who inherited his only point in his rookie Formula 1 season after Romain Grosjean was disqualified at Monza, is keen to return to the grid in the future and hopes the position at Renault can be a platform to achieve it.

However, he also spoke highly of a recent Formula E test in Marrakesh with Mahindra.

"I really enjoyed it to be honest. I was honestly never a fan of the series before, but those two weeks I worked around that project, doing the testing and some analysis after that, it really changed my opinion the opposite way around," he explained.

"I left Marrakesh with a really strong impression of how actually good the car is, and how much fun it is to drive and how good Formula E is as a series. I mean, honestly, I was quite impressed so potentially it's a future [option].

"The priority is to be back here on the F1 grid but if we see that's not going to be possible anymore, it's a great championship and [could be] a great place for me to be."