Gennett was activated from the injured list last week after recovering from a severe injury to the other side of his groin during spring training. He's 2 for 19 with a pair of singles in five games.
He flied out and struck out against Jhoulys Chacin, then left the game an inning later.
The Reds have sorely missed Gennett, who had 50 homers and 189 RBIs in the last two seasons. He was an All-Star for the first time last year, when he finished second to Milwaukee's Christian Yelich for the batting title at .310.