Harang woke Saturday morning in Pittsburgh with pain near is abdomen. He was examined later that afternoon and driven by team clubhouse manager Rick Stowe back to Cincinnati, where the surgery was performed at The Good Samaritan Hospital.
"They didn't want him to fly in case there was an emergency situation in the air," Reds manager Dusty Baker said. "Fortunately he was close enough to drive. If he got an operation he wanted to be back in Cincinnati where his family was."
The 31-year-old Harang will be restricted from strenuous physical activity for three weeks. He was to be the Reds' starter Wednesday in Milwaukee, and Baker said he isn't sure who will make the start in Harang's place.
"We're just kicking some things around," he said.
The Reds' Opening Day starter, Harang was 6-14 with a 4.21 ERA in a team-leading 162 1/3 innings. He also had 142 strikeouts in 26 starts, but will fall short of reaching 28 starts for the first time in six seasons.
Harang is the ninth Reds player currently on the disabled list, and the seventh to undergo surgery this season. Cincinnati has lost seven of eight and is 9-26 since the All-Star break, falling from 5 1-2 games out of first place to 18 1-2 and into last place.
"Whoever made up that saying, 'Injuries are no excuse' was lying," Baker said. "This is beyond ridiculous here. Wow."
It had already been announced that third baseman Scott Rolen would be activated from the disabled list in time for Sunday's game. Rolen sustained a concussion Aug. 2 when hit in the head by a pitch -- two days after being acquired via trade from Toronto.
Harang is one of only three pitchers to make four Opening Day starts for the Reds. He led the National League in wins, strikeouts and complete games in 2006 and finished fourth in the 2007 NL Cy Young Award voting.