High-A Bowling Green placed Johnson on the 7-day injured list Wednesday with right forearm inflammation, Marc Topkin of the Tampa Bay Times reports.
The Rays will send Johnson in for further imaging to determine the extent of the forearm injury, but initial X-rays apparently revealed no structural damage to his pitching arm. The 23-year-old has made seven starts for Bowling Green this season, logging a 3.00 ERA while striking out 41 over 27 innings.