The Marlins designated Mitchell for assignment Wednesday, Christina De Nicola of MLB.com reports.
Mitchell's stint on the 40-man roster and 26-man active roster lasted just under a week, with the 30-year-old right-hander sent out to clear room for starting pitcher Edward Cabrera, who is set to make his MLB debut Wednesday versus the Nationals. In what marked his first big-league action since 2018, Mitchell made two appearances out of the Miami bullpen, giving up two earned runs on five hits and two walks over four innings.