Formula 1 drivers will be "gladiators" this year as a result of rule changes that have made the cars faster, says world champion Nico Rosberg.
"The cars are going to take them to their physical limits," said Rosberg, who retired after his world title win.
"We might even see drivers losing race wins because of just being physically knackered, and that is the direction the sport should be in."
He added: "These cars are absolute monsters. It is such an awesome hype."
F1 has introduced new rules this season aimed at making the cars faster, more demanding and more dramatic-looking.
In addition, supplier Pirelli has been charged with making tyres on which drivers can push flat out for many laps at a time, which has not been the case for the past six years.
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On a visit to the first pre-season test at Spain's Circuit de Barcelona-Catalunya, Rosberg said: "There was not one moment when I thought it should be me sitting in that car. It was interesting to realise that. And perfect."
Rosberg spent time chatting to his replacement at Mercedes, Valtteri Bottas, before the Finn set the fastest time of the test so far on the third morning of four days.
Asked whether it was realistic for Bottas, who joined Mercedes from Williams, to challenge Hamilton in his first season at the team, Rosberg said: "He is a good driver so you'd expect him to be challenging Lewis. It is difficult to predict exactly how they compare.
"We all know that Lewis is a massive benchmark, so it is not going to be easy. I'd assume that sure there is going to be a good battle."