Ryu missed all of last season after having shoulder surgery in May. He threw 20 pitches in a bullpen session Monday. It was his first since Feb. 26, after which he experienced discomfort in his shoulder.
"He was a guy we had penciled in at the top of the rotation," Roberts said. "But you've got to adapt. Things are going to happen that we're not too excited about. But that's our reality."
The Dodgers' No. 3 starter in 2013 and 2014 came into camp saying his goal was to pitch in May. He also said he wanted to work 150 innings in 2016.
"To me, that's pretty unrealistic," Roberts said.