Morton lasted just two innings at Cincinnati on Thursday in the Pirates' 8-2 loss, allowing seven runs (five earned) on eight hits, and his ERA jumped to 9.35.
"Charlie has been battling mild shoulder discomfort and fatigue off and on for the majority of the season," General manager Neal Huntington said on Friday in announcing the roster move. "Charlie has not wanted to use it as an excuse and has worked to pitch through it.
"Until now, we felt we could work through the issue without risking additional damage. We now feel that the best way to get Charlie back on track is to give his shoulder appropriate rest and recovery time to allow him to get back to 100 percent."
Pirates manager John Russell revealed after the loss to the Reds that Morton had been having shoulder issues for the past few starts. But the pitcher said that he didn't feel pain while pitching and downplayed any health problems.
Clearly, the Pirates feel that Morton needs to get a fresh start mentally and physically. He will spend time in Florida while on the DL and then go out on a Minor League rehab assignment.
"I think it will be good for him," said Russell, who called Morton's time away a chance to "regroup."
"I think [with] the physical and mental drain of trying to piece it together, it will be good to get away from this atmosphere," Russell said, "to try to relax and get a little bit fresher outlook on things.
"He put a lot of pressure on himself and I think it led to the shoulder fatigue. He's been trying so hard to make things work."
Morton, 26, posted a 14.45 ERA while losing his first four starts, before getting his lone victory against the Cubs in Chicago on May 5. Although he hadn't won since, he had some encouraging outings before taking a big step back against the Reds.
Morton was acquired from the Braves last June as part of the Nate McLouth deal and went 5-9 with a 4.55 ERA in 18 starts for the Pirates. He broke into Majors with the Braves in 2008 and was 4-8 with a 6.15 ERA in 16 games.
With Morton on the DL, the Pirates are expected to call up someone from Indianapolis by Tuesday. That is when Morton's next start was scheduled to fall, with the Pirates playing the Cubs in Chicago.
Jackson, 28, was 1-0 with a 3.42 ERA in 17 relief appearances with the Indians. He was claimed off waivers from the New York Yankees last May, and he was 2-3 with a 3.14 ERA in 40 relief appearances with the Pirates.
Indianapolis was in Charlotte, and Jackson, a South Carolina native, drove to Atlanta on Friday with his wife, Lindsay, and 7-month-old daughter, Molly. They had come down for a Memorial Day weekend visit.
"I didn't start out very well this season, but it had been going real good lately," Jackson said.