Webber, a big admirer of the Ferrari driver, told reporters at the launch of the new Jaguar R5 in Barcelona that he could not see the German capturing a seventh title, and fifth in succession, in 2004.
"I think that we will definitely have a new champion this year," the Australian said. "One of the Williams drivers or Kimi (Raikkonen) will probably win the championship.
"Yes, I am a big Michael fan but I think it'll be a hard year for them (Ferrari) because I think the Michelin thing will just prove too much in the end."
Schumacher starts the season in Australia on March 7 as the sport's only active champion following the departure of Canadian Jacques Villeneuve from BAR.
The German turned around a poor start to last season, in which Williams and McLaren set the standard, to beat McLaren's young Finn Raikkonen to the title by two points, with the championship going down to the wire in Japan where he struggled home in eighth place.
Williams, with Colombian Juan Pablo Montoya and Ralf Schumacher, were impressive on Michelin tyres in the hot and dry conditions that prevailed for much of the year but Ferrari's Bridgestone tyres proved better in the wet.
Many Formula One observers expect the French manufacturer to be strong consistently this year and predict Bridgestone, now supplying only Ferrari, Sauber, Jordan and Minardi, could struggle to match them.
BMW-powered Williams have also launched one of the more radical-looking cars of recent years and have been fast from the off in testing this month.
"Michael did a phenomenal job last year to scrape that (title) out of the bottom of the can," said Webber.
"He's a racer and he loves the sport but he won't enjoy it if it (losing the title) does happen. If he does lose the championship it'll be a tough one to swallow."
Schumacher is contracted to Ferrari until the end of 2006 and has said he will continue in the sport for as long as he is still enjoying himself.
"He's been awesome for our sport and I think it's very healthy that he'll stay around for a bit longer," added the Australian.
