It was announced before Sunday's game that Bruce was scratched from the original starting lineup with left knee soreness and would be replaced by Chris Heisey in right field and the cleanup spot in the order. Cincinnati went on to a 4-3 victory over Milwaukee at Great American Ball Park.
Bruce is hitting .218 with three home runs and 14 RBIs in 29 games this season.
Bruce missed only one of Cincinnati's first 31 games this season, sitting out against Pittsburgh lefty Francisco Liriano in the Reds' 4-0 win over the Pirates on April 16.
He came off the bench in the seventh inning Sunday and struck out on three pitches in a pinch-hit appearance against Milwaukee.
The loss of Bruce is a blow to a Cincinnati offense that's tied for 10th in the National League with 116 runs scored.
He is one of only three current players (Miguel Cabrera of the Detroit Tigers and the Texas Rangers' Adrian Beltre) with at least 30 home runs in each of the last three seasons. Bruce, a two-time All-Star, averaged 32 homers and 101 RBIs per season from 2011-2013.