Pierre Gasly is set to start the Mexican Grand Prix from the back of the grid as Honda opted to revert to an older-spec Formula 1 power unit for the race weekend at the Autodromo Hermanos Rodriguez.

Both Gasly and Toro Rosso teammate Brendon Hartley started from the back of the field in Austin last weekend at the United States Grand Prix after changes, with Honda working to perfect its new ‘Spec 3’ power unit before the end of the season.

Driver Ratings - United States GP

Honda confirmed on Friday at the start of opening practice in Mexico that both drivers would be returning to an older-spec power unit for the weekend, with Gasly taking a penalty in the process in order to add another Spec 3 power unit to his pool for the remainder of the season.

“Gasly is starting FP1 with a new latest spec PU. The reason for this is that we have a concern regarding the assembly of the one used in Austin,” Honda F1 technical director Toyoharu Tanabe said.

“That PU has been sent to Sakura for a full inspection and, at the moment, we are not sure if we can use it again this year. By fitting a new one here, we add one to the pool of available units for the rest of this season.

“However, as from FP2 and for the rest of the weekend, Gasly will run an older specification PU. Brendon is also using this spec, for the entire weekend.

“The reason for reverting to the earlier pre-Russia spec is that we have a better understanding of this version of the PU and are more confident in our ability to set it up correctly for the specific conditions here in Mexico City.”

The FIA confirmed in its FP1 technical update that Gasly’s car had been fitted with a new internal combustion engine, turbocharger and MGU-H ahead of the session.