High-A Brooklyn placed Mathis on its 7-day injured list Tuesday due to an unspecified injury.
Mathis will head to the IL for the second time this season, though it's unclear if his latest setback on the health front is related to the injury that kept him out for about seven weeks earlier this summer. The 23-year-old corner infielder -- whom the Mets acquired in the June 25 deal that sent left-hander David Peterson to the Cubs -- debuted for his new organization on July 23 before being reinstated from Brooklyn's injured list Aug. 4. He appeared in just three games for Brooklyn -- going 1-for-11 with a double and 3:5 BB:K -- prior to landing back on the IL a week later.