The Dodgers announced Friday that the lefthander would be shut down for three days after receiving an anti-inflammatory injection in his throwing shoulder.
Ryu was sent back to Los Angeles to see the team's doctor.
"I think he's feeling something. If he was feeling nothing, we wouldn't be trying to get him in front of Doc," Mattingly said, according to ESPN.com. "We know to move forward it's going to be a heavier workload, so we've got to be sure where we're at. I saw the look on Hyun-Jin's face and it wasn't typical Hyun-Jin."
Ryu, who turns 28 on Wednesday, is the team's No. 3 starter. He missed three weeks in the beginning of last season and the final three weeks of the 2014 regular season with an injury in the same shoulder.
- Dan Gartland