McLaren to make double engine changes on both F1 cars at Spa

The team has fitted Alonso and Button's cars with their respective seventh Honda engines of the season for first practice after it used three of its engine token allocation for upgrades.

As Button has already taken a seventh turbo charger and MGU-H, the move to a seventh internal combustion engine will likely mean he takes a five-place drop.

Alonso has yet to use the seventh component of any element and is therefore expected to take a 10-place grid drop.

There is also expected to be changes to other engine elements, thus likely resulting in both drivers starting from the back of the grid.

McLaren then plans to perform another change after second practice, while it analyses data from the seventh engines, fitting an eighth power unit to both cars.

Under the old rules, which were tweaked mid-season, Button and Alonso would have taken heavy grid penalties with additional in-race time penalties for any position-drops that could not be served.

But following the clarification a move to the back of the grid is now the maximum penalty.

It also means that from the Italian Grand Prix onwards, the team will have two engines per car which it can use free of further penalties in their post-Belgian Grand Prix state.

"There are some races we need to sacrifice to get ready for the second half of the season, and definitely this is one of those," said Alonso.

"Maybe we are not super-competitive at this track, it's not the best layout for us, so I think it's the best place to get some penalties.

"We have to be aware it's probably not the last penalty this season.

"We have to make sure we improve the engine and the car for next year.

"So if in the remaining races we have to take penalties but the performance is increasing it is very welcome."

Button added: "We'll start at the back with penalties, but to be fair, I'd rather that and have the improved power and reliability for this weekend.

"I don't know how competitive we'll be, but with the new engine and aero updates we'll have to see.

"You'll always take the penalty if you can have more power for here and Monza."