According to Jeff Passan of ESPN, Burdi suffered a "strained biceps tendon and flexor mass" injury after falling over in pain in the eighth inning during a 12-4 loss against the Arizona Diamondbacks, but avoided any major structural damage:
Jeff Passan @JeffPassan
The plan is for Pirates reliever Nick Burdi to seek a second opinion, per source. The injury was so painful and the feeling so acute, Burdi wants to ensure that rehab is indeed the preferred course of action and he can avoid another procedure on his surgically repaired right arm.
You can see the pitch where he suffered the injury below:
"That was heart-wrenching," reliever Kyle Crick said of Burdi's injury, per Adam Berry of MLB.com. "To know what he went through the previous year to get back here, and having success in the big leagues and something like that happens, it’s tough."
"It takes the breath right out of you," Pirates manager Clint Hurdle added. "You love to compete, you love to watch young men play, then that's the hard part of it when something like that happens."
Burdi, 26, underwent Tommy John surgery in May 2017 and appeared in just two games in September of last season. In 2019, he's gone 2-1 in 11 appearances with a 9.35 ERA, 1.62 WHIP and 17 strikeouts in 8.2 innings.
He had started the season on a strong note before giving up five runs on Monday night, ballooning his ERA, and then suffering the biceps strain.
Regardless of the results of the second opinion, Burdi is still probably facing a significant stay on the injured list. But the fact that it appears he suffered no breaks or tears is the best possible outcome given how serious the injury looked when he fell to the mound in pain on Monday night.