Asked if Span was done for the year, Williams said, "It's 15 days. We have to make sure we are mindful of him, his back and his hips. So it's unclear right now. I would imagine it's going to be very tough for him to get back."
Span was activated from the DL on Tuesday after being out two months due to back tightness and abdominal issues. He played two games and went 2-for-9 with a run scored.
The Span era could be over in Washington because he is a free agent after this season and Michael Taylor is expected to be the starting center fielder next year. It's not known if the Nationals will offer Span a qualifying offer. But he has been a tremendous leadoff hitter with the Nationals, hitting .292 with a .345 on-base percentage in three years with the club.
Ryan Zimmerman made it known he wants Span to return to the team.
"It has been a tough year for him," Zimmerman said. "… You feel bad for a guy like that who goes out and plays hard every day. Unfortunately, it was always something with him. I'm sure it's frustrating for him. He is a good teammate, a friend. It is tough to see that."
The Nats will announce a corresponding roster move on Friday.
• While playing for Class A Advanced Potomac on Aug. 19, outfielder Reed Johnson was hit in the ribs by a pitch. He made it worse later in the week by sneezing and breaking a rib. He is expected to be out 4-6 weeks. Johnson was on a rehab assignment while recovering from a left foot injury.
• Reliever David Carpenter returned from his rehab assignment with Double-A Harrisburg due to a sore right shoulder, according to Williams. He is currently on a throwing program.
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.