Ladendorf, 28, has limited big league experience; he totaled four hits in 17 at-bats over nine games for the A's last year. But the club has always valued his ability to handle essentially every infield and outfield position with above-average defense.
He's also been hitting the ball well, overcoming an 0-for-12 start with Triple-A Nashville to collect a hit in eight of his last nine games, including three multihit games. Overall, he was batting .240/.269/.360 for the Sounds.
"He gives us really the type of versatility we need for both the infield and outfield," A's manager Bob Melvin said. "There are few guys that can play defense as well as he can at all of the positions, so it's obviously nice to have him here."
Ladendorf was on the A's Opening Day roster last year but was sent down less than a week into the season and suffered a broken ankle shortly thereafter, making him unavailable when the A's came calling again for a substitute for a surgery-bound Ben Zobrist. Ladendorf returned to the big league club as a September callup, and he hit .364 in 16 games this spring.
Valencia returned to the Bay Area on Friday to undergo an MRI, while Chris Coghlan remained at third base in his stead in Toronto.
Jane Lee has covered the A's for MLB.com since 2010. This story was not subject to the approval of Major League Baseball or its clubs.