2016 F1 World Champion Nico Rosberg has warned Lewis Hamilton that George Russell is 'the ultimate test' at Mercedes.
Merc have had a trying start to the 2023 campaign with them not at the same level as Red Bull in terms of performance.
Indeed, they are instead having to settle for a fight to be best of the rest up against Aston Martin and Ferrari, at least for the time being.
Upgrades and changes to the W14 are expected in the coming races and it'll be interesting to see where the car stacks up once those have been applied but, clearly, they are not quite where they want to be right now.
Work to do then, but Mercedes know that and in Hamilton and Russell they have two of the best drivers on the grid, and can also make a strong argument for having the best line-up of the entire 2023 field.
Certainly, Russell has shown he is more than at home at the front of the pack, with him winning his first Grand Prix last season in Brazil and also outscoring his seven-time world champion team-mate in the standings.
Nico Rosberg labels George Russell a 'future world champion'
Both will just be itching to see the car get back to a position where it can fight for wins regularly, then, and Rosberg has warned his former team-mate Hamilton that he must be ready for a real fight in order to remain being seen as the number one driver at Merc, given the talent Russell has:
"Testament to the weekend George has done. Interesting that there is different set-ups, but free choice for both of them," Rosberg said to Sky Sports after the Saudi Arabian Grand Prix, which saw Russell eventually classified fourth and Hamilton in fifth.
"For Lewis, it was a nice comeback today and it gives him some comfort after a dark day yesterday [Saturday.]
"George is the ultimate test, he is a future world champion. It is difficult for Lewis to stay in front. George had an awesome season last year and that is continuing.
"Let's not forget, Lewis is the best of all time, so if someone can beat George it is him.
"It is a little bit of a weakness that Lewis has that he will mentally go into this down a little bit and lose a little bit of the flow but he comes back with a bang every single time so, dear George, don't get too confident there."
Both drivers are exceptional talents, with Hamilton's place among the greats already assured and Russell aiming to try and get there in the future.
First things first, though, is that the Mercedes needs to be quicker, and we'll wait and see what they can do this weekend at Albert Park.
