Mata suffered an apparent left hamstring injury Sunday while pitching in a simulated game at the Red Sox's alternate training site in Pawtucket, Bill Koch of The Providence Journal reports.
The 21-year-old isn't a likely candidate to make his big-league debut in 2020, but he's been making regular simulated-game appearances in Pawtucket as the Red Sox look to keep his development on track. He'll presumably be sent in for more tests as the Red Sox determine the extent of his injury, but Mata looks like he could be at risk of being shut down for the rest of the summer.