Gonzalez (3-4) dropped his third straight start in Saturday's 5-2 loss to the New York Mets. He lasted only three innings, allowing five runs and seven hits, which raised his ERA to 4.62. Gonzalez gave up seven runs and nine hits in his previous start at Oakland.
The 28-year-old danced around questions about his health Saturday.
Gonzalez went 32-16 during his first two seasons with the Nationals after a trade with the Oakland A's. Sunday's trip to the DL is the first of his career.
Mattheus has 140 career appearances with the Nationals, including two this season. He has not allowed a run in three innings.
