Sale reportedly has left elbow tenderness and was not happy with the switch.
"Chris is going to be fine," pitching coach Don Cooper told reporters. "He was upset. He wanted to continue to (start).
"But again, sometimes we have to make decisions based on what we feel is best for that individual, and that's what we did."
Sale is 3-1 with a 2.81 ERA.
"We're going to be trying to make him one of the best left-handed relievers in baseball, not only the American League," Cooper said. "That's where we're at with it."
"This gives Hector a chance to pitch and go out there and develop," Cooper said. "But this is a decision based solely on Chris."