McArthur, who was placed on the 15-day injured list Tuesday, was diagnosed with a Grade 1 UCL sprain in his right elbow and will be shut down from throwing for 5-to-7 days, Anne Rogers of MLB.com reports.
The 27-year-old won't be able to return before the end of the regular season, but manager Matt Quatraro is hopeful a playoff return is possible. That's likely an optimistic outlook for a UCL injury, but for now, McArthur has yet to be fully ruled out for 2024.