Cameron suffered the injury Friday evening in Las Vegas while taking batting practice before the Padres' penultimate exhibition game of the spring against the Cubs.
"The whole thing is getting out of spring training without getting hurt," said Cameron, who is one of the key players for the Padres this season. "This is not good."
Cameron, whom the Padres acquired from the Mets last winter in a trade for Xavier Nady, hit .354 this spring and showed no ill affects from the facial fractures he suffered last Aug. 11 in an outfield collision with then Mets teammate Carlos Beltran at San Diego's Petco Park.
"This is one of the most critical parts of the body," Cameron said. "There is a lot of torque. All I can do is wait."
With Cameron on the disabled list, Ben Johnson made the Opening Day roster as the Padres fourth outfielder.
Dave Roberts will move from left back to center, with left-handed hitter Terrmel Sledge expected to get most of the starts in left against right-handed pitchers while platooning with Eric Young and Johnson. Johnson and right fielder Brian Giles will become Roberts' backups in center.
"This is really sad," said Roberts. "You come all this way to assemble a team, and Mike's such a huge part of that. To lose him for any amount of time is disheartening."
"How said is that?" veteran utility man Eric Young said of Cameron's injury. "He looked so good."
Cameron was expected to hit second in the Padres order. Sledge will likely hit there against right-handed pitchers until Cameron returns, with SS Khalil Greene or Young hitting in that slot against RHPs.