Helmut Marko has confirmed that Red Bull have got to the bottom of the fuel system issue that ruled Max Verstappen out of the Australian Grand Prix.
Verstappen had been running a comfortable second to Ferrari's Charles Leclerc with 20 laps remaining in the 58-lap race when he suddenly slowed and stopped his car at the side of the track exiting Turn 1.
It was the second dramatic DNF for the reigning World Champion in the opening three races of the season, having also retired from second place in the season opening Bahrain Grand Prix.
Both Red Bull advisor Marko and team boss Christian Horner said on Sunday evening that the suspicion for the Melbourne retirement lay in the fuel system, although it wasn't thought to be a repeat of the problem from Bahrain.
Having seen Leclerc sail to a dominant victory and extend the gap between himself and Verstappen to 46 points, Marko said: "We have a tough task ahead of us."
Marko: Verstappen's race-ending issue is very complex
Three days after the Australian Grand Prix, Red Bull appear to have found the root cause of Verstappen's issue.
Speaking to Red Bull-owned publication Speedweek, Marko didn't go as far as explaining what the specific problem was.
"We were able to clarify the cause of the fuel leak in Max's car," he said, but couldn't confirm whether the issue is likely to be rectified with a long-term fix before the Emilia Romagna Grand Prix in less than two weeks' time.
"The matter is very complex. The problem is absolutely different from that of Bahrain."
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Horner: Red Bull could see the issue developing
Horner said the team were able to spot that an issue was developing while Verstappen was still on the track.
"We could see on the data that something was wrong, and Max could smell it as well," he told media, including RacingNews365.com, after the race.
"It looks like a fuel system issue, external to the tank, so it's gone into quarantine.
"The parts will return to [Honda's headquarters in] Japan and we'll obviously try and understand the problem as quickly as we can."
F1 Podcast: Can fast but fragile Red Bull respond to Leclerc's charge?
RacingNews365.com F1 journalists Dieter Rencken, Mike Seymour and Thomas Maher look back over the Australian Grand Prix, where Ferrari's Charles Leclerc triumphed and Red Bull's Max Verstappen retired.