Emerson Fittipaldi rates Lewis Hamilton as one of the greatest Formula One drivers but thinks the Briton faces a "a lot of challenges" from his rivals this season.
Hamilton claimed his fourth world title last year and the Mercedes driver is favourite to claim a fifth this season.
Fittipaldi expects Hamilton and Mercedes to set the standards ahead of the first race of the year in Australia this weekend, but the two-time world champion is expecting an intriguing battle.
"I think Lewis with Mercedes, the combination, [in] my opinion, is still the most competitive combination of 2018," Fittipaldi told Omnisport, speaking courtesy of the Laureus World Sports Awards.
"[But] he'll be facing a lot of challenges; Ferrari is going to be very strong this year. McLaren could be strong, back again in the business, Red Bull for sure.
"I think it will be a great championship. When you are defending the world championship it's an extra challenge because you are the world champion, to defend your championship is tough. There'll be tremendous pressure on Lewis.
"I have followed Lewis since he was racing go-karts and he has had a fantastic career. He delivers. When he needs to deliver the result, he's always there. Extremely competitive, very emotional.
"The love, the passion for the sport, I can see in every mile that Lewis is driving. Every kilometre he's driving a racing car, it's there. He's a fantastic example of one of the best ever Grand Prix drivers."
Fittipaldi says the first race in Melbourne on Sunday should serve as a good indication of how the season will pan out.
"I think it will be very difficult to know now. After Australia we will have more comparison between the teams, the cars, the drivers. For sure, Ferrari is going to be very strong." the Brazilian added.
"They were strong last year. McLaren has the capacity to be strong again, with the Renault engine, a more powerful engine. Red Bull will be always there.
"I think these are the biggest challenge for Lewis and they can do well in the championship and you get a young guy like [Max] Verstappen who is starving to be champion. It will be a great show for sure."