Harper hurt his hand with a headfirst slide into third base Friday night after hitting a third-inning, bases-loaded triple in Washington's 11-1 victory. He stayed in the game for an inning before he was replaced.
"It's part of baseball. You slide into the bag and sometimes you get your fingers," Harper said. "It's a bummer, but hopefully I'll be back soon."
Harper will fly to Cleveland on Monday to see prominent hand specialist Thomas Graham for a second opinion. For now, his prescribed treatment is ice.
The Baltimore Orioles put first baseman Chris Davis on the 15-day DL because of a strained left oblique.
The move is retroactive to Saturday. Davis left Friday night's game against Kansas City after four innings and has not played since.
Baltimore did not make a move Sunday to fill the roster spot. The Orioles are off Monday, and Manager Buck Showalter said the team will fill out the 25-man roster before Tuesday's game against Pittsburgh.
Davis led the majors last year with 53 home runs and 138 runs batted in. This season he has two home runs and 13 RBIs in 22 games.