BALTIMORE - The Washington Nationals placed centre fielder Denard Span on the 15-day disabled list Friday, hoping an extended rest will help him recover from lingering back spasms.

Span was pulled in the third inning of Monday's game against Cincinnati and has not played since. He had an MRI on Tuesday and is seeing a specialist in an effort to eliminate an injury that has plagued the Nationals' leadoff hitter the entire season.

Manager Matt Williams was encouraged by the report he received on Span, which showed no structural damage.

"It's good news," Williams said. "The results of the MRI and the specialist he saw finds nothing alarming. We have to look at his history and look at the two surgeries he had this winter and say, 'You know, there's some changes in there, so we have to address them.'"

Span is batting .304 with five homers and 22 RBIs in 59 games. He's 11 for 11 in steals.

If all goes well, he will rejoin the Nationals soon after the All-Star break.

"All the news is great, so that will give him a sense of relief," Williams said. "It's certainly relief for us. And it will allow him to be aggressive in his rehab and get back in a short time."

In other moves, Washington reinstated reliever Aaron Barrett from the DL, recalled infielder Wilmer Difo from Double-A Harrisburg and placed starting pitcher Jordan Zimmermann on the paternity list.

Barrett was 3-2 with a 5.06 ERA in 30 games before missing 24 games with a right bicep strain.

This will be Difo's third stint with the Nationals this season. The rookie has played in six games.

Zimmermann's wife gave birth to a girl on Monday. He is expected to return Saturday to start against the Orioles.