Ferrari has fitted a new power unit - featuring an updated hybrid system - on Charles Leclerc and Carlos Sainz’s cars at the last two races in Russia and Turkey, resulting in back-of-the-grid starts at both events.

The Italian outfit has remained tight-lipped about the exact gains it has made with its new engine, though it is understood to be worth around 8-9bhp. 

Ferrari held a performance advantage over McLaren in Turkey as it cut its deficit by 10 points and closed to within 7.5 points of its direct rival in the battle for third place in the constructors’ championship. 

“At some races we have still been better and at some they have been better,” Norris said ahead of this weekend’s United States Grand Prix. 

“As a trend they have been on the stronger end, especially now with the new power unit it has definitely shifted their pace into a stronger one. 

“If you look at Turkey there are not one or two tenths ahead, they are a fairly large chunk ahead of us. They definitely have a very competitive car, and a more competitive power unit now. 

“It is going to make our life tougher but the aim is still to beat them, and will put everything into staying ahead of them in the championship. It is going to be difficult and we will fight hard to the end.” 

Despite the Circuit of the Americas being a track that is expected to suit McLaren’s car better than Istanbul Park, Norris was keen to avoid making any predictions about how his team will fare this weekend. 

“On some areas of the track we can be good and in other areas we will struggle,” he said. "Just from what we have learned, some are good and some are bad. 

“Whether the good parts top the bad parts, or whether the bad parts override the good parts, we will have to wait and see. 

“But it is not just the track, there are some other variables, the bumps, the wind, the temperature. We think we will be okay but it is very close, so it's not like we know that we will be two tenths quicker than Ferrari or two tenths slower. 

“We think we can have a good weekend and we aim for a strong weekend and hopefully be better than we were in Turkey.”