Dr. Tim Kremchek, the Reds' medical director, performed the operation.
"He said everything went well," general manager Walt Jocketty said. "It went as expected and the surgery was routine."
Bruce is batting .216 with three home runs, 14 RBIs and a .352 on-base percentage in 30 games this season. He was scratched from the starting lineup before Sunday's 4-3 win over the Brewers because of left knee soreness. Bruce pinch-hit in the bottom of the seventh inning and struck out.
The exact details about how Bruce was injured were unclear.
"I think it's something he's had for a while. It inflamed on him," Jocketty said. "I'm sure he did it playing, but we don't know when."
For the injury-riddled Reds, Bruce is the 11th player to go on the DL this season, which is barely a month old. He joins other key players who are currently out, including closer Aroldis Chapman, catcher Devin Mesoraco and starting pitcher Tony Cingrani.
Although Bruce had yet to heat up at the plate, losing a two-time National League All-Star is a big blow for Cincinnati both offensively and defensively.
"It's tough. We've just got to keep fighting," Jocketty said. "Somebody has to pick up the slack, that's all. All those guys will have a chance to get better by playing more."
Chris Heisey, who has delivered several clutch hits as a pinch-hitter this season, is the Reds' fourth outfielder and could pick up some of the slack. Skip Schumaker was activated from the disabled list on Saturday after he missed the start of the season with a dislocated left shoulder, which occurred during Spring Training.
When Schumaker rejoined the team, Roger Bernadina was designated for assignment. The club also announced on Monday that Bernadina cleared waivers and had accepted an outright assignment to Triple-A Louisville.
That means Cincinnati could bring Bernadina back to the big leagues on Tuesday since the 10-day rule required to stay in the Minors after being sent down doesn't apply when someone is injured. Jason Bourgeois, another Louisville outfielder with big league experience, is a possibility, but he would have to be added to the 40-man roster.
Another option is Double-A Pensacola outfielder Donald Lutz, who is hitting .389 and played in the big leagues last season. However, Lutz has only played in one game since April 24 because he also was on the DL.
The Reds were already shorthanded in the outfield with rookie center fielder Billy Hamilton missing the past three games with two sprained knuckles on his left hand. It wasn't yet clear if Hamilton could return to the lineup on Tuesday.
"He hasn't made a ton of improvement," Jocketty said. "We don't anticipate it's a [DL situation], otherwise we would have done something for sure."