"This is the final stages of what he's got to do," Collins said. "I know he's going to be fine. He felt great yesterday with everything he did."
Collins suggested previously that d'Arnaud's rehab assignment could be as short as eight to 10 at-bats.
d'Arnaud has been out since May 13, when Alfonso Soriano's backswing caught him in the back of the head.
Tim Healey is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.