KANSAS CITY, Mo. (AP) — The Royals expect to place left-hander Bruce Chen on the disabled list with a swollen disc in his back that has already caused the club to juggle its starting rotation.

Chen was supposed to throw a side session Thursday, but manager Ned Yost said the 37-year-old left-hander was in pain even before he made it to the mound. Chen’s anticipated move to the DL means that Yost will have to find someone else to start in his place Saturday against Detroit.

Yost was still mulling his options before Thursday night’s series finale against Toronto, but he did acknowledge that left-hander Danny Duffy could move out of the bullpen.

Chen said he’s been dealing with back pain for weeks. He’s already had an epidural to relieve some of the swelling, but so far it has not made the pain subside.