The Twins announced late Tuesday they'll designate Johnson as their 26th player for the second game Thursday, the rescheduled slot for the game that was washed out Tuesday. The move was made to avoid using Wednesday starter Kyle Gibson on short rest later in the week.
Johnson was acquired in a trade with Pittsburgh last November. The 29-year-old made four appearances last season for the Pirates in his major league debut, including one start. This year, Johnson is 2-2 with a 2.86 ERA in four starts for Triple-A Rochester.