A Lake Elsinore spokesperson told the San Diego Union-Tribune on Friday that "Johnson called trainers and coaches out to the mound after his last pitch -- a single to right field -- and then headed toward the clubhouse after brief conversation."
Johnson had thrown one-inning simulated games leading up to his rehab assignment.
The 31-year-old right-hander hasn't pitched in the big leagues since 2013. It's been a long road since his April 24, 2014, surgery. Johnson had hopes to make it back for the 2015 season, but he suffered a setback in April.
Before heading out for his rehab assignment, Johnson said he felt good and was hopeful he would be able to compete again.
"Being here, showing up every day, working hard, [being able to pitch again] would make it kind of easier to go through," Johnson said on Tuesday. "It's been tough, it's been a long road, but things happen for a reason. I don't know why right now, but it's all part of it."
Beth Maiman is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.