Dodgers manager Dave Roberts said the discomfort is considered normal and is not a setback.
"We're just backing off because he felt something, but this is all part of our cautious plan to bring him back slowly," said Roberts. "It's not a setback."
Ryu didn't sound particularly worried when he said he's "just following the pace of what they told me" after his second bullpen session.
"There's definitely no pain," Ryu said. "A little typical soreness. I'm very happy and satisfied with the timetable. Even after my Tommy John surgery [which he had in high school], there were good times and bad times. I'm sure the next [bullpen session] will be very soon."