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.