Chen progressing with first bullpen session

KANSAS CITY -- Bruce Chen saw his first action on the mound since a bulging disc in the Royals starter's back forced him to the disabled list.

Chen threw a 16-pitch bullpen session on Wednesday morning.

"It felt good, I feel like I'm making a lot of progress and I'm just very happy about how everything's going, and I'm very grateful to the medical staff for guiding me through this process and getting me better to the point where I can throw in front of the mound," Chen said.

Chen said he did not know when he would make a rehab start.

"We haven't discussed [that]," Chen said. "Once I start throwing a couples sides and everything goes well, then maybe we can start thinking about what's the next plan."

Danny Duffy is expected to make Chen's scheduled start on Saturday against the Orioles.

"I didn't want to push it," Chen said. "This is the first time throwing from the mound, and the best thing is to do things that don't irritate the nerve."

Chen logged a 7.45 ERA in his first four starts this season.