The move came just hours before McDonald was scheduled to pitch on Tuesday night against the Seattle Mariners. Jeanmar Gomez will start in McDonald's place.
The 28-year-old McDonald is 2-2 with a 5.76 ERA in six starts this season. He was rocked in his last start in Milwaukee on April 30, giving up seven runs on eight hits in five innings. His velocity has also dipped this spring, though McDonald has insisted he was not concerned about his health.
McDonald's move is retroactive to May 1. He will miss at least one more start.
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