"You've got a guy throwing into the mid-90s who runs it up right into your ribs. That can't feel very good," Padres manager Bud Black said.
Eckstein sported a bruise on the left side of his chest and appeared to be shaking off soreness as he worked out during batting practice, but he also took several robust swings and was able to drive the ball well.
Black said he leaves it up to the player's discretion whether to play.
"I trust the player on this," Black said. "As long as there's no risk of him making it worse."
Eckstein popped out on a bunt attempt in his first at-bat and handled a pair of grounders on defense in the first inning.
David Brown is a contributor to MLB.com This story was not subject to the approval of Major League Baseball or its clubs.