Waldrop, who was placed on the disabled list retroactive to March 26 with a strained right elbow, made four rehab appearances with Class A Advanced Fort Myers.
He tossed four scoreless innings, allowing two hits while striking out five and walking one. He made two appearances in mid-May before returning to Minneapolis to have a precautionary MRI on his elbow on May 21. But the MRI showed no new structural damage and he returned to Fort Myers, where he tossed scoreless innings on Sunday and Tuesday.
"I think he's throwing the ball pretty well," assistant general manager Rob Antony said. "He's throwing strikes. He's been efficient. The main thing is he felt good."
To make room for Waldrop on Rochester's roster, the Twins released right-hander Daryl Thompson. They also released Brad Thompson, who was pitching at Double-A New Britain.