After changing the engine at the Mexican GP, ​​Norris will start at the end of the grid

To date, the Briton was the only Mercedes engine that had not exceeded its allocation of three engines.

But after a tricky opening day in Mexico City, Norris is expected to be at the bottom of the grid along with Aston Martins Lance Stroll and AlphaTauris Yuki Tsunoda.

Although there is still no official confirmation of the change, sources have revealed that a decision has been made.

Since three drivers opted for a penalty lap this weekend, the last starting positions are based on their times in qualifying – an incentive for them to go out on the track and set lap times.

Norris’ move to get a fourth engine should be good enough to see him through by the end of the campaign. Teammate Daniel Ricciardo added an additional engine to his pool at the Turkish Grand Prix.

While McLaren has opted for the fourth engine in Mexico, the factory Mercedes teams still hope that it can avoid having to strive for a fifth engine with World Cup hopeful Lewis Hamilton.

Lando Norris, McLaren MCL35M

Photo by: Glenn Dunbar / Motorsport Images

There are only five races left and Mercedes is grappling with some concerns about the reliability of its internal combustion engine.

At the weekend in Mexico, however, Mercedes boss Toto Wolff expressed the hope that the situation would improve after the latest work in the engine department.

“I think we feel more resilient to a particular problem that seems to be resolved,” he said.

McLaren is in a very close battle with Ferrari for third place in the constructors’ championship, with only 3.5 points separating them.

Ferrari has made some good strides in the performance of its own propulsion unit over the past few weeks, and McLaren thinks its rival has some momentum behind it at the moment.

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However, McLaren hopes the extra power Norris gets from running a new engine could prove helpful in the closing stages of the campaign.

Norris, who starts from the bottom of the grid, also opens up the prospect that McLaren can use him to offer a towing service to Daniel Ricciardo in Q2 which could prove helpful in increasing the Australian’s straight-ahead speed.