Nico Rosberg claimed that his lack of pace during qualifying at Monza was due to his old engine, but Niki Lauda begged to differ.
The German's new-spec power unit (PU) suffered a failure during FP3 on Saturday morning and Mercedes decided to put an old engine in his car ahead of qualy.
While his team-mate Lewis Hamilton, who had the new-spec PU at his disposal, went on to claim his 11th pole position of the season, Rosberg could only manage P4 as Ferrari's Kimi Raikkonen and Sebastian Vettel were also faster than him.
Rosberg was adamant afterwards that his woes were down to the old engine.
"We had to go back to an engine that has done six races now and, every kilometre, you lose a bit of power so," he told Sky Sports. "Especially at a track like Monza, the absolute power track where you need a good engine, so it's very disappointing to have it happen here.
"It's a very big compromise and the reason why I am fourth today, which makes the race tomorrow tough as I will be slower in the race tomorrow as well. That's not ideal and will be difficult against those Ferraris."
However, Mercedes non-executive chairman Niki Lauda believes Rosberg just couldn't come to grips with the handling of the car.
"Nico was not down on power, he had handling problems – too much understeer, he complained about it," he is quoted as saying by Motorsport.com. "He couldn't get the car to handle properly for his way of driving and this made a huge difference."