(Reuters) - Baltimore Orioles ace Chris Tillman is headed to the 15-day disabled list with shoulder inflammation, the team said on Tuesday.

Tillman was scheduled to pitch on Thursday against Washington but felt pain in his shoulder during a bullpen session and received a cortisone shot.

"I thought once it got loose it would really go away, but it never really did, and that was my first time actually experiencing it while throwing," Tillman told reporters after the Orioles' 8-1 win over the Nationals on Tuesday.

"Last time, I was pretty sore right after my start, but after feeling it today, I'd much rather just get this behind us and get out in front of it so that way we're not worried about it for the rest of the year."

Tillman, tied for third in the American League with 15 wins, had a start pushed back by three days last week because of right shoulder discomfort.

For the season, the right-hander is 15-5 with a 3.76 ERA.

(Writing by Jahmal Corner in Los Angeles; editing by Sudipto Ganguly)