Racing Point driver Sergio Perez has been forced to switch back to Mercedes' older specification Formula 1 engine following a failure in Belgian Grand Prix practice.
The failure will be a cause for concern for Mercedes, as all six drivers from the works team, Racing Point and Williams took the new upgraded spec on Friday morning - which comprises a V6, turbo and MGU-H - at Spa.
An investigation into the failure - which struck Perez towards the end of the second 90-minute session on Friday - at the Mercedes High Performance Powertrains factory in Brixworth is ongoing.
Fortunately Perez still had mileage on his last old spec engine, which was set to be used up over future race weekends, and will not take any grid penalties for the change.
However, he now looks set to take a penalty at Monza next week if as expected he takes a new example of the latest spec, which will be his fourth PU of the year.
"I just got off the power and I saw a little bit of smoke and noise coming out of the exhaust, so not looking good," said Perez, who was fifth at the end of FP2.
Despite the frustration with the engine issue, Perez was encouraged by the performance of the car, which is running a new front wing and other updates.
"I think it's helping the balance," he replied when asked by Autosport about the wing.
"But I still think there is a lot of work to do. I think we are getting there, step by step.
"It's looking promising for the weekend and we can be strong tomorrow when everyone puts it together.
"I think we are doing good progress, I think historically this is a good circuit for us so I'm not surprised we are competitive. I found a very strong rhythm today and things are looking very solid."
Team-mate Lance Stroll reported a burning sensation in his back during FP2, which was related to excessive heat from electrical boxes behind his seat, and not connected to the problem Perez suffered.