Brown hurt his ankle on March 1 and did not play in another Grapefruit League game before being sent to Minor League camp Thursday.
Rizzo did not know if Harper would be ready for Opening Day with Class A Hagerstown. Harper sprained his left ankle during a Minor League intrasquad game at the Washington Nationals Training Complex on Monday morning.
According to an eyewitness, William Yoder, Harper hit a ground ball to short and didn't appear hurt until his foot hit the first-base bag.
Harper was carted off the field and immediately examined by the Nationals' training staff. He is currently listed as day-to-day.
"It's not a mild sprain. It's called a medium sprain, but everything checked out fine," Rizzo said. "It's similar to what Brown went through."