Harrell was designated for assignment on April 16 after opening the season 0-3 with a 9.49 ERA. The terrible start to the season stretched his losing streak to eight straight decisions and he has not won a start since June 15. He led the American League last season with 17 losses.
He cleared waivers on April 22 and was sent to Triple-A Oklahoma City.
The 28-year-old Harrell, who has been both a starter and a reliever, is 18-33 with a 4.84 ERA in 88 career games with 62 starts.