The Reds placed Johnson on the 15-day injured list Saturday, retroactive to Wednesday, with right elbow inflammation.
Johnson's injury helps to explain why he hasn't pitched in a game since Tuesday. He received a cortisone shot in his right elbow Saturday, and with the MRI results coming back negative, Johnson expressed optimism about a minimum-length stint on the IL, per Charlie Goldsmith of Fox 19 Now Cincinnati. Tony Santillan figures to handle a larger share of high-leverage opportunities while Johnson is out, and Lyon Richardson will come up from Triple-A Louisville to fill the void in Cincinnati's bullpen.