Prepared for the worst but hoping for the best, the A's were forced to face the undesirable of the two outcomes Monday evening, when they learned third baseman Scott Sizemore will miss the entire 2012 season with a torn ACL in his left knee.

Sizemore suffered the injury Saturday afternoon within two hours of the club's first full-squad workout, and on Monday morning he underwent an MRI administered by Dr. Douglas Freedberg that revealed the fateful news.

Due to swelling, the 27-year-old infielder will have to wait two weeks before being reevaluated to determine when he can undergo surgery. Meanwhile, the A's will turn to a catching prospect for help, with Josh Donaldson expected to get a long look at third base before the club decides whether to look outside the organization to fill the void.