"He was pretty sore," Nationals manager Matt Williams said. "He tried to get loose [on Saturday], and he couldn't get loose."
After Saturday's game, Harper said he didn't feel well.
"It's more spine than back, so it's more a bruise in the spine," Harper said. "I'm going to take it day by day and see how it feels."
Harper is not sure if he will play Sunday against the Reds.
"It's not really a muscle thing or anything like that. It's that bone. It's not fun to go through," Harper said. "It's more of that bone bruise kind of feeling."
In the seventh inning of Friday's game, with Denard Span on second, Cingrani replaced right-hander Jumbo Diaz to face Harper. On the first pitch, Cingrani hit Harper, who was clearly upset. Harper threw his bat near the Nationals' dugout and slowly walked to first, where he exchanged words with first baseman Joey Votto.
After the game, though, Harper sounded as if he understood Cingrani wasn't trying to hit him on purpose.
"Just got away from him," Harper said. "It's part of the game. Just got away, nothing I could do. Just hit me."
In Harper's place on Saturday, Clint Robinson was moved from left to right field, while Michael Taylor replaced Harper in the lineup.
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.