Denard Span had surgery Monday to repair a right core muscle injury and will miss the start of the season for the Washington Nationals.

Matt Williams said the projected time for Span's return is uncertain and added "you're looking at four-to-six 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.

"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."