Uehara, who went 2-4 with a 4.05 ERA, will leave the team for good this weekend.
"We're going to send him back to Baltimore, and then he'll pack up some things and he can go back home to Japan," said manager Dave Trembley. "He will not pitch for the rest of the year. He has given us the information that he's not ready. His elbow is a bit sore, so we're running out of time. He originally asked if he could take a week or so off with no throwing and then maybe start up from there. That just runs out of time for us."
Uehara went on the disabled list in late June and spent more than two months attempting to get his elbow back to pitching condition. The right-hander, who went through a long throwing program at the team's Minor League complex in Sarasota, Fla., is disappointed in the way his debut season has gone.
"Right now, I'm not in a stage where I can throw in a game situation," he said through interpreter Jiwon Bang. "There's still a discomfort in my elbow, and I'm not in a position not only to throw to a batter, but to throw 100 percent."
Uehara made 12 starts with the Orioles but hasn't won since the second week of April. The 10-year veteran of Japan's Central League spent two weeks on the DL with a hamstring injury in early June, and he made only a few starts before going back on the shelf with an elbow ailment.
Uehara was told at the time that rest, rehabilitation and a strengthening program would heal the injury, and he said on Friday that he sees no reason why he would ultimately require surgery.
"When I took the [MRI]," he said of his initial prognosis, "the team doctor as well as the second-opinion doctor told me that it's not necessary, so I don't think so."
Trembley began to have doubts about Uehara earlier in the week, when Uehara threw a bullpen session at Fenway Park and couldn't manage better than around 50 percent velocity. Now, said Trembley, the main goal is to get Uehara healthy and involved in a December throwing program to prepare him for Spring Training.
"I am not upset. Surprised? I'm not so sure. It's hard for me to say anything," said Trembley. "It's unfortunate, because we were all looking forward to getting him back and maybe getting him some time in the bullpen to see if that would be a little better fit for Koji and the club. We can't do that now, so I think it's unfortunate. The key thing, and it's what we told Koji, is make sure we get him healthy and make sure he's ready 100 percent for Spring Training."
Uehara, who spent most of his time in Japan as a starter, was expected to pitch in relief for the Orioles down the stretch in preparation for his role next season. He has said that he's OK with that plan but that he'll continue to prepare as a starter, and he said on Friday that his first season is hard to evaluate.
"To be honest, I couldn't do a good job. Obviously, it's a disappointment," he said. "I'm upset because I wasn't able to contribute to the team. It's a lot of minuses, so I can't really assess my season."
Spencer Fordin is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.