Mike Trout last played for the Angels on July 12, when he left a game against the Astros with what was then diagnosed as back spasms. According to team trainer Mike Frostad, the condition is actually something far rarer, though it is unclear how long it may keep the superstar outfielder out of the team’s lineup.

“This is a pretty rare condition that he has right now in his back,” Frostad said. “[Dr. Robert Watkins], one of the most well-known spine surgeons in the country, if not the world, doesn’t see a lot of these. For it to happen in a baseball player, we just have to take into consideration what he puts himself through with hitting, swinging on a daily basis just to get prepared and then also playing in the outfield, diving for balls. Jumping into the wall, things like that.