Fernando Alonso will start the Belgian Formula One Grand Prix near the back of the grid after the Spaniard’s McLaren team replaced his power-unit with a fresh one following yesterday’s opening practice session.

The double world champion and his team-mate Jenson Button switched to the fifth of their permitted five power units heading into the weekend with engine-supplier Honda introducing an updated version.

But Alonso’s sprung a water leak during yesterday morning’s 90-minute practice session, limiting him to just three laps with no time on the board. The new power unit, which will cost Alonso 35 places on the grid, is of the same updated specification Honda has introduced this weekend.

Marcus Ericsson will also drop 10 places on tomorrow’s grid, after his Sauber team fitted a sixth turbocharger to his Ferrari-powered car.

World championship leader Lewis Hamilton is also set for a hefty grid drop for exceeding his permitted allocation of engine components.

The Briton is already set for a 30-place grid drop, with Mercedes fitting his car with two new power units ahead of each of yesterday’s practice sessions.

The possibility of Hamilton taking on a third new power unit ahead of today’s final practice session to push him even further down remains open, a team spokesman said.

The Formula One grid comprises 22 cars.  Grid penalties cannot be carried over to the next event which means Hamilton, Alonso and even Ericsson are likely to start together at the back in tomorrow’s race.

But just where they line up relative to each other will depend on when they were hit with their respective penalties, the number of places they have to drop and where they qualify.