A.J. Puk, who was slated to be the Oakland Athletics' fifth starter, has been placed on the injured list with a shoulder strain.

The left-hander will see Dr. Neal ElAttrache and Bob Melvin admitted there is "a level of concern" during a conference call.

"The fact that we have to put him on the (injured list) right away, obviously there's a level of concern. We want to make sure we get this right before we throw him back out there again," Melvin said. "... It's frustrating for him because he went through this in the spring."

After he was officially named the club's No. 5 starter, Melvin announced Tuesday that Daniel Mengden would replace Puk.