Nico Rosberg is to take a new upgraded engine at the Singapore Grand Prix, as Mercedes continues its investigations into the unit that was damaged at Monza.
The German was forced to revert to an older specification power unit for the Italian Grand Prix after a leak in the cooling system of his new engine led to problems in final practice.
Rosberg faced further trouble in the race though, with the older unit failing in the closing stages and costing him a podium finish.
Early analysis of the removed Monza engine has suggested that it can be used again, but the team is still not sure about whether its performance will be compromised of if there are reliability risks.
The power unit is set to be fired up ahead of the Singapore Grand Prix so detailed checks can be done, after which a decision will be made on where and when the engine can be used again.
It is possible that the engine could be given the all clear to run in Friday practice, but it is highly unlikely that the team will want to risk running it in the Singapore race.
The uncertainty means that Rosberg will therefore take his fourth power unit of the season for the Marina Bay race, which will be to the updated specification that was introduced at Monza.
With seven races remaining, Rosberg will need at least two engines to see out the season, so if the Monza unit is not cleared to race then it means he will face a grid penalty later in the campaign if he has to take a fifth unit.