The 35-year-old former two-time Cy Young Award winner was attempting to come back from shoulder surgery and was slated, after two rehabilitation starts, to join the Orioles in roughly two weeks.
Santana was supposed to throw between 75 and 85 pitches in one final extended spring training Friday, but threw only 33 in three innings. He was struck on the backside by a liner, and when he attempted to retrieve the ball, he injured the Achilles, Orioles manager Buck Showalter said.
Santana had allowed just one hit while striking out three and walking none.
The Orioles purchased Santana’s contract June 2, and he was expected to make two minor league appearances before joining the Orioles, potentially as part of a six-man starting rotation.