Riley, 22, has homered 13 times in his last 18 games at Triple-A Gwinnett, including a grand slam Tuesday at Buffalo. He is batting .299 with 15 homers, 39 RBIs and 32 runs in 37 games.
Outfielder Ender Inciarte left Tuesday's 14-3 loss to the St. Louis Cardinals with tightness in his lower back and was placed on the 10-day injured list on Wednesday.
Riley has been blocked at third base in Atlanta by Josh Donaldson, but Inciarte's injury opens a spot for him in left field with Ronald Acuna Jr.