Burdi has a strained biceps tendon and flexor mass but may be able to avoid surgery, Jeff Passan of ESPN.com reports.
Burdi appeared to suffer a serious injury Monday against the Diamondbacks, going down in obvious pain after throwing a pitch. An MRI revealed no full tear or fracture, so he appears to have avoided the worst-case scenario. He's out indefinitely, and the Pirates would be wise to treat him with caution, as Burdi has thrown just 21 innings since undergoing Tommy John surgery in 2017.