Stammen was placed on the disabled list Wednesday with "forearm tightness." The team called up right-handed pitcher Taylor Jordan to take his place.
Stammen has pitched for the Nationals since 2009, posting a 3.91 ERA. In 2012 and 2013, he had a combined 2.54 ERA in 170 innings. He had thrown four scoreless innings so far this season.
The right-hander had never been on the disabled list before feeling tightness in his arm during his outing Sunday, according to the Washington Post. He pitched again Tuesday but felt sore and indicated to the Nationals something was wrong. An MRI on Thursday revealed the flexor tear.
- Alex Putterman