Thompson, who was placed on the 10-day injured list earlier Sunday, was diagnosed with right biceps tendinitis after undergoing an MRI, Jessica Camerato of MLB.com reports.
The original diagnosis for Thompson's injury was a biceps strain, but it's instead been classified as tendinitis after receiving the imaging results. It's unclear how long the 24-year-old is expected to be unavailable, but he'll be eligible to be activated April 20 versus the Diamondbacks.