The Reds selected Aguiar's contract from Triple-A Louisville on Monday, Charlie Goldsmith of The Cincinnati Enquirer reports.
Aguiar will make his major-league debut Monday in Toronto, taking the rotation spot of the injured Hunter Greene (elbow). The 23-year-old has split his 2024 season between Louisville and Double-A Chattanooga, collecting a 3.79 ERA and 95:29 K:BB over 116.1 frames between the two stops. Aguiar should have an opportunity to make at least one additional start later this week, which would come in Pittsburgh.