"It was determined he has irritation to the UCL [ulnar collateral ligament] but no structural damage was found," said a statement issued by the team Thursday. "He is expected to go through two to three weeks of strengthening exercises, then begin a throwing program."
The elbow problems initially developed for Eaton in March, and he was shut down and placed on the disabled list.
Had this recent setback not occurred, it appeared Eaton would have been able to rejoin the D-backs before the end of the month.
"It just feels like someone punched me in the stomach," Eaton said Wednesday before seeing Lee. "It's tough to have a setback like this, but I have to try and learn what I can during this and go forward. Try to take as much good out of a bad situation."
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.