Williams suffered another problem with its Mercedes power unit on the final day of Formula 1 pre-season testing but George Russell has played down the issue having made up for lost time.

Following murmurings of frustration growing at Williams due to reoccurring engine stoppages across testing, Russell reported an unidentified but small issue during the afternoon of the last day of the second test at Circuit de Catalunya-Barcelona which disrupted his race simulation.

While the root of the issue remains unclear, Russell says power unit suppliers Mercedes will produce a full investigation into its ongoing issues and iron-out the problems ahead of the 2020 opening race.

“We had a small issue with the engine in the afternoon, but we had a good morning [where we did] a quali simulation with our turnaround. I think it was good preparation ahead of Melbourne,” Russell said.

“I just get in and drive, I leave that to the guys at Mercedes and here. Obviously not ideal, but it’s one of those things. Mercedes is pushing the limits at the moment, and I’m sure they’ll go back and review everything.

“It made some funny noises and I started losing a bit of power. I don’t know if there’s an official word.”

Having got back to the Williams garage after detecting the issue, the team was able to find a solution which allowed Russell to return to track action and complete the bulk of his test programme with 146 laps on the final day to see the total laps completed by Williams reach 737 over the two tests.

“We had planned to do two full race sims, and we got one-and-a-half in,” he said. “Still loads of laps. We still got a full race sim in at the end of the day, I think, I don’t know exactly.”

Deputy team principal Claire Williams remains optimistic Mercedes can fix the ongoing issues before the Australian Grand Prix which starts the 2020 F1 season on March 15.

“Unfortunately, some of our run plans were impacted by the number of engine reliability issues that materialised over the six days and which primarily affected Nicholas's [Latifi] running, but we have every confidence that Mercedes HPP will resolve these prior to actually racing,” Williams said.

“It’s still early days, but the car certainly looks better than last year’s and that’s what we wanted to demonstrate, that we can make progress.”

Earlier this week, Williams couldn’t hide her frustration at the reoccurring engine issues as the team looked to make a fresh start following its nightmare 2019 which was triggered by missing the opening two-and-a-half days of pre-season testing due to delays in completing its car.

“I think everyone’s probably a little frustrated because we’ve obviously got - as everyone will - a very full programme to get through,” Williams said on Wednesday.

“When you lose the number of kilometres that we’ve lost it is frustrating, because it just means you can’t prepare as best as you’d like to do ahead of going to Melbourne.”