Middleton (ankle) threw 38 pitches in a live batting practice session Friday.
Middleton landed on the injured list after he was forced to leave a game July 25 against the Giants with a right ankle strain. Arizona manager Torey Lovullo said the reliever "felt good" following Friday's session and added a progression for the right-hander has yet to be determined. The manager said Middleton will probably eventually throw in the rookie-level Arizona Complex League.