Third baseman Ryan Zimmerman broke his thumb on this play against Atlanta last month. (Mike Zarrilli/Getty Images)

Ryan Zimmerman underwent his weekly follow-up X-ray on his fractured left thumb, and the bone has not yet healed enough for the third baseman to begin strengthening exercises, Nationals Manager Matt Williams said. Zimmerman broke his right thumb on April 12 diving back to second base on a pickoff.

Zimmerman was expected to be out four to six weeks. It has only been a little more than four weeks since his injury. Williams said the doctor wasn’t ready to clear Zimmerman to begin hand activities. Zimmerman will continue to work out and do conditioning exercises, but can’t hit or throw.

“I’ll imagine we’ll get back to that in about a week and see where he’s at,” Williams said. “Good callous, good healing. But it’s only been four weeks. He’s not quite there yet. He doesn’t want to risk re-injuring it and having a setback at this point. All the other stuff he can do.”

>>> Nate McLouth would normally be starting against a right-handed starter, such as Tuesday’s pitcher Bronson Arroyo. But because the scab on his right hand tore open Monday night, McLouth is receiving treatment and out of the starting lineup, Williams said. 

McLouth ripped his scab open during batting practice but even deeper during the game. McLouth originally cut his hand badly on May 5 when he made a spectacular diving catch and slammed into the left field wall at Nationals Park. After the hand healed some and was bandaged up, McLouth returned to action but aggravated the injury on Monday.

McLouth is available off the bench on Monday, Williams said, but perhaps mostly as a defensive replacement. Gripping a bat and throwing a ball are difficult with the wound in between the pointer finger and thumb.

At the plate, McLouth has been scuffling. He snapped an 0-for-19 skid on Monday with a single. But overall, he is hitting .091 for the season (5 for 55 with one home run). He is working to improve his swing and timing, but his hand has limited the progress.

“His key is staying on top of the baseball,” Williams said. “His power is pull power, gap over here, line drive to left, to his opposite side. He’s hit a lot of flyballs to left. And for him, that won’t translate because that’s not great power that way. His power is pull power. He’s been working on staying on top of the baseball. The other day he lined out. [Monday], he hit a groundball, stayed on top of the groundball back through the middle. So it’s coming, but he’s working hard at it every day.”

>>> Bryce Harper recently had the stitches removed from his left thumb, on which he underwent surgery to repair a torn ligament on April 29. Harper has yet to begin any rehab work, according to Williams, because the thumb is still healing.