Johnson (elbow) is scheduled to throw a bullpen session March 23, the San Diego Union-Tribune reports. The mound session will mark Johnson's first since he underwent his second career Tommy John surgery close to 11 months ago. Johnson has been long-tossing in camp without issue, and is slated to throw to a catcher on flat ground several times before advancing to elevated ground. It appears the right-hander is on track to be ready for big-league action around late May or early June, barring a setback.