Reddick, who was activated Tuesday, was sidelined June 29 with the right knee strain after sitting out June 1-23 with a hyperextended knee.
Manager Bob Melvin plans to have Reddick — who will wear a brace — in the lineup often because of his bat and defensive presence.
Reddick is hitting .229 with four homers and 24 RBI in 54 games this season.
The 27-year-old left-handed batter, who made his major-league debut with the Boston Red Sox in 2009, features a .238 career batting average with 58 homers and 202 RBI. He's played with the A's since 2012, hitting .235 with 48 homers and 165 RBI in 324 games.