Parker has been diagnosed with a Grade 3 UCL sprain in his left elbow and is likely to undergo Tommy John surgery, Mark Zuckerman of NatsJournal.com reports.
A full Tommy John repair could sideline Parker until 2028, though he would have a chance to make it back late in the 2027 season if all goes well. The left-hander has collected a 6.58 ERA and 34:13 K:BB over 39.2 innings out of the Washington bullpen this season. Parker is slated for arbitration eligibility for the first time this coming offseason, though he could be a non-tender candidate.