Harper was given the shot after he visited noted orthopedist Dr. James Andrews on Monday in Pensacola, Fla. Trainer Lee Kuntz said Tuesday Harper will stay off the knee for a week.
"We'll reevaluate him in one week's time to resume activities, so these are all good things," Kuntz said.
Kuntz said that Andrews confirmed the original diagnosis made by team doctors that Harper, who is on the 15-day disabled list, has patellar bursitis.
Harper was given the injection after consulting with the team's doctors, hoping it will help ease the pain and swelling. Harper also was advised to wear a heavy brace on his knee so he doesn't place it under too much stress.
"We want him to rest the knee. That's why we put him in the immobilizer," Kuntz said. "It's kind of a reminder for him to stay off it."
Harper was photographed with his knee wrapped and wearing the brace, setting off Internet speculation that he had some sort of surgery. But Kuntz reiterated that was not the case.
Also, Nationals manager Davey Johnson said right-hander Stephen Strasburg, who is on the DL with a lat strain, threw a simulated game Tuesday and came out of it well.
"He threw about three or four innings; had no pain," Johnson said. "He came out of that good, so he should be back soon."