Jenson Button set for 50-place penalty, at least 10 for Alonso

Honda and McLaren have concluded their investigations into the issue that caused Fernando Alonso to slip from a points-scoring finish in last Sunday's race at Austin to out of the points in 11th.

In using the new 'phase four' power unit across the weekend for the first time, Honda discovered a fault with the injector that has since been rectified.

Although Honda is confident there will be no repeat, it is changing Alonso's internal combustion engine to his 11th of the season, which means a 10-place grid penalty.

Alonso also faces a further potential five-place hit for a gearbox change, although a firm decision on that has yet to be taken.

As Honda discovered no serious fault with Alonso's system, Button's car will be fitted with a new engine, turbocharger, MGU-H and MGU-K ahead of first practice as planned to bring him onto the phase four spec too, incurring a 25-place penalty.

Ahead of second practice, exactly the same components will be replaced to create a greater pool that can be used in the remaining grands prix, but incurring an additional 25-place demotion, resulting in 50 overall.

Come the conclusion to the weekend Button will also have used 11 apiece in terms of the engines, turbocharger and MGU-H, and 10 of the MGU-K.

Button has confirmed with the Mexico track not suiting the car, it is another opportunity to take the penalties now ahead of the final two races of the year in Brazil and Abu Dhabi.

"It's not a great way to start the weekend," said Button.

"But then it's going to be a very difficult weekend for us anyway. Because of the altitude it hurts us with the compressor, more than other teams.

"It's obviously low downforce here, and we pretty much have max downforce on the car, everyone will have, but because of the air pressure we are running Monza downforce if you like.

"Quick in a straightline, not a lot of air into the brake ducts, so there are a lot of unknowns for everyone here.

"As long as we're on top of that, we might be OK in the race, but in terms of pace it's going to be tricky for us here."

Following the summer rule tweak regarding how large grid penalties were fulfilled, the McLaren drivers should simply start at the back at Mexico City.

Well until this season's Hungarian Grand Prix, a grid penalty that exceeded the number of places on the grid would result in further time penalties being applied throughout the race.

But that's all changed, and now McLaren are exploiting the relaxing of the punishment to implement their new engine, turbocharger, MGU-H and MGU-K, knowing that they'll only have to start at the back of the grid with no further penalties.