"You know a lot more once you're in there," Reds manager Bryan Price said. "There are some issues in there that aren't going to get better through strength and stretching and things of that nature."
Marshall had a 7.71 ERA -- with 23 hits, 12 earned runs, 12 walks and 14 strikeouts -- in 15 games over 14 innings. He retired only five of 15 first batters faced, and five of his 11 inherited runners scored.
Shoulder problems limited Marshall to 16 games last season, and he began this season on the DL when he had more issues during Spring Training. When he returned on April 19, he still lacked velocity and any real consistency. Marshall was placed on the DL again last Friday.
"It's definitely not something I'm excited about," Marshall said of the surgery. "I've been able to stay off the surgery table my whole career and I've never been on the surgery table before in my life. I'm pretty nervous about it, but I think in the long run it'll help this team win some games. The doctors are very confident in what they can do and how they can make me feel."
Joining Marshall on the 60-day DL is right-handed reliever Trevor Bell, who has been out since April 8 with elbow trouble. Bell had been on a rehab assignment at the team's complex in Arizona.
"His elbow got sore again. They found that he probably was going to need Tommy John surgery," Price said.
And in one more transaction, starting pitcher Brett Marshall was activated from the 60-day DL and optioned to Triple-A Louisville.
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, and follow him on Twitter @m_sheldon. This story was not subject to the approval of Major League Baseball or its clubs.