Madson pitched an inning for Class A Inland Empire as part of a rehab assignment on May 13 and felt inflammation in his right elbow over the following days.
The right-hander, who had Tommy John surgery and has not pitched in a Major League game in more than a year, felt normal soreness after his outing, but he said the feeling remained on Friday.
"Waiting for it to calm down," Madson said. "After Monday's game, it got inflamed again and it hasn't calmed down yet. I think we've reached another plateau."
Prior to this "plateau," Madson was scheduled to go on a rehab assignment with Triple-A Salt Lake. Madson still plans to go to Salt Lake and will make multiple appearances there, but it remains to be seen when he will take the mound.
"I can't believe it's taken this long," Madson said. "I thought by last Friday it would be ready."
Although things certainly have not worked out as planned, Madson continues to believe he is close to returning as he reached another "high point" in the recovery process prior to this setback.
Before Monday's rehab appearance, Madson had been on an aggressive throwing program and acknowledged he may have overworked his elbow, but he also said any number of things could have been the culprit.
"It could be the workload was too much, the intensity was too much," Madson said. "In between, I was long tossing to get the arm strength and velocity up -- which I did. Could have been mechanical, dropped my arm slot a little bit. It might have been mechanical, a little tired. It could have been two or three different things or a combination of."
William Boor is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.