Mercedes has traced the cause of Nico Rosberg's reliability issue on Saturday to leak in the cooling system, which then contaminated the power unit itself.
Rosberg had to revert to the power unit he used at the last five races ahead of qualifying, which is a specification that has not benefited from Mercedes spend of seven tokens ahead of this weekend. Rosberg was down on power as a result and qualified fourth, while Hamilton, with a brand new engine fitted, took pole position.
Mercedes' investigation traced the issue to the cooling system, meaning it was not a problem with the power unit itself.
If the issue had been linked to a problem with the engine, Mercedes would have considered changing Hamilton's power unit ahead of the race, resulting in a pit lane start, but the team is now confident the issue will not occur on Hamilton's car.