The A's are "hoping for the best," said manager Bob Melvin, "but it was tough. Watching the video, it breaks your heart."
The video of Parker's injury is not easy to watch. The right-hander is shown clutching his elbow while collapsing to the ground, writhing in pain following a wild pitch -- his 87th pitch of his Friday outing, coming in the sixth inning with Triple-A Nashville.
You can not play this media on the current browser / platform.
Jarrod Parker leaves with injury
More info
It was the fourth rehab start for Parker, who is attempting to return from a second Tommy John surgery at age 26.