Mercedes are still scratching their head over Nico Rosberg's engine problem at Monza with Toto Wolff admitting there is a "big question mark" over their new power unit ahead of the race.
The Merc works team introduced a new-spec engine ahead of the Italian Grand Prix, but Rosberg suffered a problem ahead of qualifying and the team opted to put an older engine in his W06.
The German then endured a pretty disappointing qualifying session and will start Sunday’s race in P4, behind his team-mate and pole-sitter Lewis Hamilton as well as the Ferraris of Kimi Raikkonen and Sebastian Vettel.
Wolff revealed on Saturday evening that they still have to get to the bottom of the problem and says there are no guarantees that Hamilton's new engine won't have similar issues.
"We simply don't know what the root cause of the problem on Nico's engine was and we don't think it is performance related," he said.
"We haven't yet identified the problem so there is still a big question mark about what's actually happened and the potential risks for Lewis tomorrow."
He added: "It was clear today that even if we would have found out what the problem was, we couldn't change two engines. So we did it on Nico's car.
"If we find out that it is a major issue and this is something that would put Lewis's engine at risk and Lewis's race at risk this would certainly be something we would consider because our car has great pace and it is better to play it safe.
"But at this very moment we don't know that and I still have the belief that it's something we can solve."