The six-wheeled robot slipped back as it tried to drive out of the crater Sunday. The dry, sandy soil and a 16-degree slope caused the rover to spin its wheels, NASA's Jet Propulsion Laboratory said.
Controllers planned to try a second way out of the crater Monday driving the rover diagonally across the slope.
"We know the vehicle can do this sort of thing," project manager Richard Cook said. He added: "There are many, many variations on this that can be done before we get worried."
Opportunity has encountered previous problems with slippage inside the crater but never as severe as those that stymied it Sunday, Cook said.
Opportunity landed inside the 72-foot-diameter crater on Jan. 24.
Halfway around Mars, Opportunity's twin rover, Spirit, has been exploring the rim of a far larger crater.
NASA launched the twin, $820 million mission to search Mars for evidence the planet once was a wetter place. Opportunity already has uncovered such evidence.
NASA scheduled a Tuesday news conference in Washington to announce what it called another "major scientific finding" by the mission.
Scientists are expected to provide more details about the watery conditions under which rocks found at Opportunity's landing site were formed.