On the disabled list since May 2, retroactive to April 28, Willingham talked about a best-case scenario being late May or June 1.

Willingham has been nursing a strained lower back. Last September, he was out of action because of a herniated disk.

"I think it's all correlated together," Willingham said. "What happens is, if you irritate the disk, it pushes on the nerve, and how the back reacts to that, is the muscles around it tighten up."

Willingham was eligible to be reinstated on Tuesday in Cincinnati, but he received a setback while taking a few swings in the batting cage on Monday. Before that bump in the road, the team was looking to get Willingham in a few rehab assignment games by Friday.

That timeline was thrown off course when Willingham aggravated his back injury.

"In my opinion, I might have been a little overanxious," he said. "I tried to do too much too soon, maybe, as far as swinging activities. Now I'm dealing with it."

Willingham has appeared in 25 games, and he was hitting .341 with six homers and 16 RBIs when he went down.

The Marlins were rained out on Thursday at Cincinnati, and the team will open Interleague Play on Friday against the Royals at Dolphin Stadium.

Willingham likely will see a doctor in the next couple of days to get another medical opinion. He consistently states that the back won't require surgery.

Recently, he received an epidural injection in his back.

This story was not subject to the approval of Major League Baseball or its clubs.