General manager Ruben Amaro Jr. announced the decision Monday. He said an MRI revealed a "very mild" strain and the team will take a "conservative approach" by skipping Happ's turn in the rotation on Wednesday. Philadelphia opens a three-game series in Atlanta on Tuesday.
Happ will throw a bullpen session on Thursday. He's 1-0 and hasn't allowed an earned run in 10 1/3 innings in two starts. Happ was 12-4 as a rookie last year.