"It's just flared up, and I was out there hobbling. It didn't feel good," Span said. "It has been bothering me with certain movements, like trying to accelerate."
Span said there is nothing structurally wrong with the knee, but he has to keep a close eye on it.
"I have to get treatment on it, get anti-inflammatories on it and hope [the pain] goes way," Span said.
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.