Garrett was diagnosed with a left elbow impingement last week, Christina De Nicola of MLB.com reports.
Garrett missed multiple months of action with a strained left forearm before suffering a setback with his elbow during a bullpen session in September. He is currently going through a throwing progression at the Marlins' spring training complex in Florida, and the setback isn't considered something that will jeopardize his availability for the start of spring training.