Helmut Marko concerned about Mercedes' potential

Helmut Marko admitted to being concerned about Mercedes' "dangerous potential".

Mercedes has yet to challenge Red Bull and Ferrari for pole or victory in the first seven races of the season.

But in practice at recent races in Miami and Spain, Lewis Hamilton and George Russell have managed to greatly narrow the gap to the leaders.

"Mercedes is doing incredibly fast laps in practice and also in races, both with Hamilton and Russell," Marko told Formel1.de."

"Not continuously, so for us it is difficult to interpret where that lap time comes from. Listening closely to the Mercedes people, I don't think they know either."

"But the dangerous thing is that the potential seems to be there. And once that can show up from one race to the next, they'll be up there or in front."

Both Russell and Hamilton have been able to extract a strong pace from the W13 at times in the car's race setup, but neither has been able to sustain the performance for long.

Asked if Mercedes bluffed about its speed all season, Marko added: "No, it's not a bluff."

"And it's really incredibly hard to understand when this car is incredibly fast. They were the fastest on the grid at one stage or another, but it didn't last long."

"What exactly changes there, why they are not continuously fast - thank God, - is still the problem, I would say."