Hamilton said at the last race in Saudi Arabia – where he finished seventh, 31 seconds behind third-placed Leclerc – that the season ahead was looking “painful”.
He is two places and 16 points behind Leclerc in the championship.
But Russell said that critics of the time it is taking Hamilton to adapt to Ferrari were “underestimating how difficult Formula 1 is”.
“Sometimes you can just jump in and it clicks, and it’s straightforward,” Russell said. “Other times, it doesn’t click.
“The second seat at Red Bull (alongside Max Verstappen), why has that never worked out? It’s because Formula 1’s bloody difficult.
“You know, you’re going up against the best drivers in the world and Charles is one of the best in the world, in a team that he’s been for his whole career, in a car that he knows exactly how to get the most out of.”
Russell also said that the quality of Leclerc’s driving this season should not be underestimated in any assessment of Hamilton.
“Charles has also gone a bit under the radar this year,” Russell said. “He’s having an immense season. He had a strong race in China with a broken front wing. He had a super-strong race in Bahrain and arguably the safety car stopped him from beating me. He could have had three podiums this season.
“Charles has been doing a mega job and you’d also be questioning Charles if a driver comes in and is on his pace straight away.”
Russell added that Hamilton getting back to his best was “all psychology – it’s not about working harder. It’s about your mental state. If you’re not happy, it’s difficult to drive quick as well.”
Hamilton’s struggles have led some to question whether he is past his best.
He struggled against Russell in qualifying last year, too, losing the head-to-head battle 19 times to five at an average advantage over the season of 0.171 seconds. They won two races each and Russell finished a place and 22 points ahead in the championship.
In their first two seasons together, the pair were separated by mere hundredths of a second on average in qualifying, Russell finishing ahead in the championship in 2022 and Hamilton in 2023.