Catcher Josh Phegley was admitted into a San Francisco hospital Friday night and diagnosed with synovitis in his surgically repaired right knee, the A's announced in a statement.
Synovitis is inflammation of the synovial membrane in the knee, and typically is very painful upon movement. Phegley was given IV antibiotics and is resting comfortably, according to the release.
The team is awaiting more information to decide a further course of action.
Phegley has endured roadblocks in his recovery since undergoing surgery in early July to remove a cyst in the cruciate ligament in his knee. He was originally set to begin a rehab assignment Saturday before experiencing more swelling in his knee.