Harper, who left tonight's game midway through the sixth after grounding out to first base, was diagnosed with a bad bruise on his left side, manager Davey Johnson said following tonight's 2-0 Nats win.
It appears that Harper has avoided any serious injury, including anything affecting his oblique, according to the Nationals. Harper's status is day-to-day.
"They're putting him on medication and doing a lot of treatments for him," Johnson said. "We'll see how he feels tomorrow. He didn't want to come out of the ballgame, but I saw him grimacing and I was concerned about him playing. We couldn't take a chance on it. He could pull a lat or something and he could be out for a long time. We'll take it day by day."
The bruise was originally suffered last night when Harper collided with the right field wall while attempting to make a home run-robbing catch. Harper then aggravated the injury when checking his swing during that sixth-inning at-bat. He tried to hold up on a curveball from Braves left-hander Paul Maholm and grimaced as he brought the bat back.
"I think yesterday played a part on it, but the check-swing, I think having all the force going towards the ball and then just stopping, immediately it just got me a little bit," Harper said. "Got me to the point where I couldn't breathe real quick, and had to catch my breath. It didn't feel very good."
Johnson said that Harper likely won't need an MRI, but there's a good chance he'll be held out of tomorrow's series finale with the Braves.
"You worry about it because it's a real bad contusion in there and with all the blood in there it could cause some other problems and he could hurt himself," Johnson said. "So we'll take it day by day and we'll check him tomorrow, but he'll probably be out of there."
In typical Harper fashion, he plans on trying to talk his way into tomorrow's game despite the injury.
"If I can play tomorrow, I'm gonna play," Harper said. "If they put me in the lineup, I'm gonna play. I can play with pain and I can tolerate pain, so hopefully there's nothing that can keep me out of that lineup tomorrow. ...
"Hopefully I can come in tomorrow and feel like a million bucks and play."
Harper went 0-for-2 with a walk and a run scored today, dropping his average to .337 on the season. He leads the Nationals with nine home runs and 18 RBIs.