The German, chasing his sixth successive title and eighth in total, said his team's decision to start the season with a modified version of last year's car had put them on the defensive.
"Running the old car will move us a little bit backwards compared if we had been able to run the new car," the German told a news conference.
"But it was a decision we took because we feel getting more time for the new car will make it arrive at a higher level than if we had it here and we might never have achieved that level if we had it at the first race."
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The delay should allow the team ultimately to make a far greater leap forwards in a season marked by rule changes to cars' aerodynamics, tyres and engine longevity.
However Ferrari technical director Ross Brawn suggested last week that the debut could be brought forward to the third round in Bahrain next month if rivals made the old car look uncompetitive.
Asked whether the decision meant he had less chance of winning in Melbourne, where he has triumphed four times in the last five years, Schumacher replied 'yes'.
"But, as I said before, you do not win a championship just by winning the first race," he added. "You have to look at the whole season and (find) a strategy for what you want to achieve.
STILL HOPEFUL
"I might still win (on Sunday)," added Schumacher. "That's what we are here for but our chances are less than if we had a new car because the competition has increased their game."
Schumacher said rivals had done 'a rather poor job compared to us' in recent years but that was changing.
"I believe they will have learned from their mistakes and from what we've seen from winter testing it looks like they have created quite a competitive package," he said.
"To me Renault and Mercedes (McLaren) look to be the best prepared teams."
Schumacher, now with 83 career wins, took 13 of Ferrari's victories last season and is the longest reigning champion in Formula One history. Yet he shrugged off a suggestion that winning might have become boring.
"I have enjoyed every race I have won because it is always different," he said. "You never know what is going to happen. Be sure this year will be a tough fight but we can still do it."
The German will be the oldest driver in Sunday's race but retirement remains a way off.
"I still love the sport," said Schumacher. "That is enough reason to keep on going plus I live in a wonderful time with a great team. We have a great relationship. I am 36 but only 36. I love what I am doing."