Mat Latos' topsy-turvy spring training has hit another pothole.

The 23-year-old ace of the Padres' pitching staff has suffered a shoulder injury and will not make his scheduled final spring start today. Latos said the team's medical staff described the injury as an inflamed bursa sac.

The bursa sac is a pocket of fluid on top of the rotator cuff.

"He's a little sore," manager Bud Black said. "It just sort of popped up."

It's unknown how severe the injury is or when Latos will pitch again. He was expected to start Thursday's season opener in St. Louis.

Latos said his shoulder started hurting when he lifted his arm to open a car door Wednesday, two days after his last start. He said that by Thursday, "It felt like … everything locked up. It felt like a huge piece of glass or something sharp was inside my shoulder. There was no strength to lift it."