Koji Uehara is planning to have surgery on his left knee during the off-season. He told fans, through a post on his blog, that he started having problems with his knee before the start of the All-Star break and that he had to make adjustments to his delivery that took something away from his pitches and threw off his balance. He relied on taping and pain killers during the season, but decided surgery was his best option because the knee was beginning to hamper his daily routine.
Uehara is not ready to retire, but avoided making any definitive statements because he was uncertain about his options, especially with the surgery at his age. He ended his post by thanking fans for their support this year.
[UPDATE 10/23 @ 10:38am]
The Yomiuri Giants announced that Uehara had surgery on his left knee at a hospital in Tokyo on October 23.
Source: Yomiuri 10/23/2018