WASHINGTON centerfielder Denard Span had surgery yesterday to repair a right core muscle injury and will miss the Nationals' opener next month.

Manager Matt Williams said the projected time for Span's return is uncertain and added "you're looking at 4 to 6 weeks before he can start doing baseball activity again."

Span had surgery to repair a sports hernia injury in December and reported discomfort at the start of spring training, which he attributed to offseason training.

He went 1-for-2 in the Nationals' spring training opener on March 5.

"He thought it would work itself out," Williams said. "Once he ramped it up in the first game and tested it coming out of the box, he felt it a lot more so we decided to get it looked at. Ultimately, with all the results, had to get it fixed, make sure he's good to go."

Washington outfielders Jayson Werth and Nate McLouth are rehabilitating from offseason shoulder surgery. Williams said Michael Taylor is likely to get the majority of time in center while Span is sidelined.

Noteworthy

* Cincinnati Reds catcher Devin Mesoraco is sidelined indefinitely because of a mild concussion that he suffered when a foul ball hit him on the mask.

Mesoraco was hit on Saturday during a spring training game against Kansas City and was held out of a game the following day. Mesoraco said that it's a mild concussion and has left him a little hazy.

He's being tested daily and is confined to riding a stationary bicycle and walking on a treadmill to stay in shape.

* Free-agent righthander Roman Madrid has been suspended for 50 games under baseball's minor league drug program following a positive test for a banned amphetamine.

The suspension will start when he signs with another major league organization.