Right-hander Jeremy Beasley had his contract selected from triple-A Buffalo and will be active for Thursday's game versus the Chicago White Sox.
Ryu exited Wednesday's start against the Chicago White Sox with forearm tightness after throwing four innings and 58 pitches.
Ryu left his previous start after five innings because of elbow tightness.
On Wednesday, Ryu sat 87.6 m.p.h. with his fastball and 77.8 m.p.h. with his changeup, both a 2-mph reduction from his season averages. And he threw only one cutter in the outing, which sat right up over the heart of the plate and was dropped over the left field wall by AJ Pollock.
This will mark Ryu's second stint on the injured list this year. He was out three weeks in late April and early May with elbow inflammation.
Ryu is 2-0 with a 5.33 ERA in six starts this season.