Gibson -- who was projected to be a first-round pick, possibly in the top 10, despite having seen a dip in his velocity in his last two starts -- experienced tightness in his forearm following his last postseason outing, a May 30 start against Monmouth University in the NCAA regional tournament.
At this point, the news could be a lot worse for Gibson, since the injury as diagnosed would not require Tommy John elbow ligament replacement surgery and his recovery time will be much shorter.
In his last two starts, a combined 14 innings of shutout ball, Gibson's fastball was clocked in the low-to-mid 80s, a significant drop from his usual low-90s radar gun reading.
Lisa Winston is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.