MESA, Ariz. (AP) — Chicago Cubs starter Matt Garza will undergo tests to determine the severity of the injury he sustained while pitching batting practice.

Garza, who made just 18 starts last season because of an elbow injury, felt a twinge in his side while throwing on Sunday. The Cubs called it a "mild strain" but general manager Jed Hoyer said Monday that the right-hander will undergo an MRI so team doctors will have a better sense of how long Garza will be sidelined. Hoyer said Garza will need a "rest period" and the tests should reveal "how long that is."

Garza went 5-7 with a 3.91 ERA last year. He made his final start on July 21, when he left a game in St. Louis because of a "stress reaction" in his elbow.