The Tigers brought Reed back to the majors before they opened a series at the Chicago White Sox on Friday night. Right-hander Jose Ortega was designated for assignment to create a spot on the 40-man roster.
Reed, 28, was facing third-degree criminal sexual conduct charges before a judge said Aug. 21 that the testimony of the woman who accused him wasn't credible and prosecutors failed to show that force or coercion took place.
Reed is 0-1 with a 4.88 ERA in 27 games with the Tigers this season.
Reed replaces left-hander Kyle Lobstein, who was sent to Toledo after Thursday's 3-2 victory over the Yankees.