It’s understood the team discovered a hydraulic leak in the Spaniard’s power unit system following FP2, forcing them to break the pit-lane working curfew for the second time this season in order to complete the required work ahead of final practice.
Alonso’s car has been fitted with an eighth internal combustion engine, 10th turbo, 10th MGU-H, eighth MGU-K, seventh battery store and sixth control electronics unit of the season, which combine for a total of 35 dropped grid places.
Renault's Jolyon Palmer will also start towards the back of the grid after getting a 20-place penalty. His car was fitted with its fifth internal combustion engine, sixth turbocharger and sixth MGU-H.
Alonso and Palmer join Toro Rosso's Carlos Sainz and Mercedes' Valtteri Bottas in going into qualifying with a grid penalty hanging over them. Sainz has a 20-place grid penalty for power unit component changes, while Bottas was forced to take a new gearbox ahead of the mandatory six-race cycle.