Celebrations for Yamaha's first MotoGP 1-2-3 finish since Australia 2014 at Jerez on Sunday were tinged with concern at having already 'lost' three engines.

Franco Morbidelli was the latest victim, suffering a near-identical race exit to countryman Valentino Rossi one week earlier at the same circuit.

Morbidelli lost power as he accelerated along the main straight on lap 16 of 25. The Petronas rider had been holding fourth place, between Rossi and Maverick Vinales.

The retirement not only denied Morbidelli a potential first-ever MotoGP rostrum but, with Ducati's Francesco Bagnaia later black-flagged from second with his own engine issue, prevented what could well have been a perfect Yamaha 1-2-3-4.

MotoGP teams without concessions (Honda, Ducati, Yamaha and Suzuki) are allowed to use five engines per rider during the current 13-round season. Engine design is sealed at the start of the season and, due to the extended 'Covid' technical freeze, cannot now be changed until the end of 2021.

Normal practice would see a MotoGP team 'open' (use) two engines per rider at round one, replacing them on a 'one out, one in' basis as they introduce the third, fourth and fifth engines at regular intervals during the season.

Apart from Yamaha, all other riders used the bare-minimum of two engines during the opening two rounds.

Things first went wrong for Yamaha during free practice for the Spanish GP, when a problem with 'Engine 2' for Vinales meant he was forced to 'open' a third engine for FP4.

The situation then got worse for Yamaha when team-mate Rossi's bike came to halt on the main straight, while in tenth place, during the season-opening race.

With the M1 engines seeming to shut down (rather than explode in a cloud of smoke and oil) a sensor issue is high among the current list of suspected possibilities.

If a factory is lucky, they can identify and fix glitches without needing to break the engine seals and therefore, if undamaged, potentially return the engines to action, even if only for free practice use.

But the seriousness of the problem facing Yamaha was underlined when both engines were returned to Japan for a full autopsy, meaning they were officially 'withdrawn' after round one and cannot be used again.

Yamaha also responded by giving all four of its riders two new (unused) engines for this weekend's second round, with even the third engine opened for Vinales in FP4 being parked.

But that still didn't prevent Morbidelli's bike being left powerless just over halfway through the race. The engine he was using had only taken part in three previous track sessions.

"They are checking what happened. My bike just shut off when I was going on the straight and I had to stop. But we really don't know at the moment," Morbidelli said.

"It came out of the blue. I just felt the engine wasn't going anymore and I shut the bike because I didn't know what was going to happen. So it wasn't a real 'breakdown', it was just something wrong."

Since Morbidelli has an A-Spec bike - rather than the Factory-Spec used by race winning team-mate Quartararo, plus Monster Yamaha team-mates Vinales and Rossi - the part that failed looks common to all.

"My engine is also an updated engine [over last year]. But I don’t know if it's the same spec as the three Factory guys," Morbidelli said.

Yamaha Racing managing director Lin Jarvis told BT Sport: "Obviously we lost two engines in the first race. We've just lost another in the second. So cause for concern, for sure.

"We already have ideas from the engines we sent to Japan, obviously Frankie's will be shipped tonight or tomorrow. But it's a cause for concern and that's all I can say at the moment."

The penalty for a rider exceeding the MotoGP engine limit during a season is a pit lane start, 5 seconds after the green light. The penalty is then repeated for each engine taken above the allocation limit.

With Quartararo (50 points) and Vinales (40 points) now first and second in the world championship - and holding a healthy early advantage over both injured reigning champion Marc Marquez (0 points) and triple title runner-up Andrea Dovizioso (26 points) - the pressure is on the Yamaha engineers to solve the problem before Brno on August 7-9.

Should Yamaha conclude they have no choice but to modify their homologated engine design, on the grounds of safety, they would need to get 'unanimous consent of the MSMA MotoGP Commission'.

MotoGP Technical Regulations:

'Exceptions can be made for sealed [engine] parts that are solely associated with safety issues and which have no performance benefit, which may be changed during the approval period with the unanimous consent of the MSMA MotoGP Commission.

'Such exceptions will be on a strictly limited basis to correct a proven problem which may have safety implications (eg. a faulty batch of parts, with supporting documentation from the parts supplier to identify the problem).

'Engines already sealed, including used engines can be updated in this way with the unanimous consent of the MSMA MotoGP Commission and under supervision of the MotoGP Technical Director or his staff.

'If a competitor intends to modify the approved engine in this way he must provide precise details of the planned changes to the MSMA MotoGP Commission. In each case, only the approved changes may be made.'