Nationals' Denard Span undergoes surgery on core muscle

Nationals outfielder Denard Span underwent surgery to repair his right core muscle Monday, the team announced.

Span underwent surgery to repair a sports hernia in December, but it's not clear if the two procedures are related. He played in just one spring game, going 0 for 2 Thursday.

Manager Matt Williams said the timetable for Span's recovery is up in the air, but it could be four-to-six weeks before he's ready to resume baseball activity. The outfielder is expected to rejoin the team by the end of the week to begin the rehab process.