The Twins announced the news on Thursday.
Fox made only one appearance for Minnesota, an emergency start last Friday after the Twins exhausted their bullpen and used three starting pitchers the previous night. It was quite the appearance, too, a major league debut of 5 2-3 innings, four hits and two runs allowed in a game the Twins won 4-3. He left the mound to a standing ovation.
Fox was designated for assignment on Sunday and removed from the 40-man roster to make room for outfielder Ben Revere, who was brought up from Double-A the same day.
Fox went 6-9 with a 3.95 ERA in 123 innings for Triple-A Rochester.