The Reds placed Aguiar on the 15-day injured list Tuesday with a right shoulder sprain.
It's unclear how long Aguiar's shoulder has been an issue, but he was rocked for seven runs over four innings versus Atlanta his last time out. The right-hander will conclude his rookie season with a 6.25 ERA, 1.33 WHIP and 19:12 K:BB over 31.2 innings of work. Carson Spiers is likely to slide into Aguiar's rotation spot this week.