Span has been dealing with back spasms since June 7 against the Cubs. There were times he would feel better, play a few games and then the back spasms would reoccur.
Span went to Dallas on Thursday to get his back checked.
"The appointment went well," the source said.
Span had already announced that he is not going to play in the three-game series against the Orioles this weekend. Despite starting the season on the disabled list because of abdominal surgery, Span was productive during the first half, hitting .304 with five home runs, 22 RBIs and a .367 on-base percentage.
In other news, the Nationals announced that left-hander Gio Gonzalez will start Friday's game against the O's. The team, however, did not announce the rest of its rotation for the weekend.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the Time. He also can be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.