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"Froome has been very good all season but if I didn't think I could beat him I wouldn't have any motivation to come here," he told a news conference on the Mediterranean island of Corsica.
The Spanish rider, who won cycling's greatest prize in 2007 and 2009, is viewed as the main challenger to Britain's Froome, who was runner-up last year behind Bradley Wiggins.
But this year's Tour is the 30-year-old Spaniard's first since returning from a ban for a doping violation that saw him stripped of his win in 2010 and first place awarded to Luxembourg's Andy Schleck.
Contador has also yet to register a win this season, trailing behind Froome in Oman, the Criterium International, Tour of Romandie and the Criterium du Dauphine.
There have been doubts about his fitness after he said during the Dauphine that he was only at 75 percent of his capacity.
Nevertheless, Contador said he was happy to return to "the biggest race in the world" and was hoping to perform to the best of his abilities when the riders begin the 100th edition in Porto Vecchio on Saturday.
"It's difficult to say but I'm more or less at 90 percent of my form. That was the aim for the start of the Tour, especially when you see the route," he added.
Not being favourite did not change much, he added.
"I'm the one who puts pressure on myself because I want to give the best of myself," he said.
"That's no different from other years. There'll be more than two figures in the race. Tactically, we'll decide after the second time-trial.
"Depending on my position in the overall classification, we'll choose whether to adopt an attacking or defensive strategy.
"In any event, there'll be more action, more movement on this Tour than in previous years."
Contador said that his Saxo-Tinkoff team was stronger than his last appearance in 2011, which was reassuring and could give him an advantage, particularly going into the mountain stages.
One secret weapon could be Michael Rogers, who formerly rode for Froome's Team Sky and has the inside track about how the British outfit thinks and races, he added.
