Mercedes is grappling with new engine problems as a direct result of the epic title scrap with Red Bull.
That is the claim of Red Bull's top official Dr Helmut Marko, amid reports Lewis Hamilton could go tumbling down the Turkish GP grid order due to an unscheduled engine change.
Auto Motor und Sport quotes a Mercedes team insider as confirming that while the new engine is actually unlikely in Istanbul, the change is very likely to occur immediately after that in Austin or Mexico.
"It probably won't happen in Turkey unless Lewis has a problem there," the source said. "We expect a close race against Red Bull.
"But then it (the engine change) has to be done. We're trying to do it on a track where we are either particularly strong or weak. Or when it rains.
"Mexico will be a Red Bull circuit because of the altitude, and maybe also Interlagos."
Marko thinks Mercedes has been caught out with engine issues in 2021 due to the close and intense battle for the world championship.
"Mercedes used to have an easy time," he said.
"They accelerated in the first few laps and then turned the engines down. That is no longer possible," added the Austrian.
"Now they have to drive more often and for longer in a higher mode. And then the problems come."
Red Bull sources report that Mercedes' specific problem is the crankshaft and valve seats, compromising horsepower when engine mileage starts to build up.
Mercedes team boss Toto Wolff said: "It's small things but unfortunately they're always different. There is no clearly recognisable pattern."
He admitted that an imminent engine change for Hamilton is "possible".
