Pastor Maldonado will start the Malaysian Grand Prix with a new Renault engine.
Williams has confirmed that the change was necessitated by piston damage detected after qualifying.
Under the regulations, each driver is allowed to use eight engines per season with the new unit being the second, so Maldonado will not incur a grid penalty for the change.
Any engine removed at this late stage cannot be used again for qualifying or the race.
But the problem is not too severe to prevent the engine being refitted for practice session use later in the season.
"After qualifying, some damage to the pistons was detected so we changed the engine as a precaution," a spokesperson said. "The engine will be used again in practice, as was the plan after this race anyway."
Maldonado will start Sunday's race from 16th place, with teammate Valtteri Bottas lining up 18th.