Harper, the National League rookie of the year last season, hasn't played for the Nationals since May 26 because of bursitis in his left knee. He was injured May 13 when he collided with the outfield wall in Dodger Stadium.
The Chicago Cubs designated former All-Star closer Carlos Marmol for assignment, and the team has 10 days to trade or release him or send him to the minors if he clears waivers. Marmol, 30, was 2-4 with two saves and a 5.86 earned-run average this season. . . . New York Yankees third baseman Alex Rodriguez, who had left hip surgery Jan. 16 and hasn't played this season, tweeted that his surgeon has cleared him to play in rehabilitation games. . . . Arizona activated second baseman Aaron Hill, who hadn't played in the majors since April 9 when he suffered a broken left hand when hit by a pitch from Pittsburgh's James McDonald. . . . Boston optioned struggling third baseman Will Middlebrooks to triple-A Pawtucket (R.I.).