Haren has been battling a shoulder injury, Nationals manager Davey Johnson told Charlie Slowes of 106.7 the FAN:
...in lieu of some of his latest outings, it's apparent that he has a little shoulder weakness. And we're going to put him on the DL to let him recover a little bit and get right, because I definitely need him.
Washington signed Haren in the off-season to a one-year, $13 million contract. The veteran has struggled this year, going 4-9 with a 6.15 ERA in 15 starts. Haren's K/9 and BB/9 numbers are in line with his career averages, but he has struggled with the longball this year, surrendering 19 home runs in 82 innings.
The right-hander battled back issues last season, which helped contribute to a 4.33 ERA in 2012, his highest single-season ERA since 2004. Haren did bounce back in the second half of last season, posting a 3.58 ERA in his final 73 innings, so the Nationals can hope the starter makes a similar recovery this year.
The Nationals have not announced a replacement for Haren in the rotation, although Johnson did mention Ross Ohlendorf as a potential candidate to start. Ohlendorf made a spot start on June 12 against the Colorado Rockies and only allowed one run over six innings.