The team said Thursday he tore his elbow tendon again while rehabbing. The Royals had been optimistic he would return in May. Then he experienced soreness while throwing recently and the team ordered an MRI.
The 26-year-old left-hander has not pitched since Game 6 of the 2014 World Series. His initial reconstructive elbow surgery came during spring training in 2015.
Collins led American League relievers with 93 strikeouts in 2012 and was 12-17 with a 3.54 in 228 bullpen appearances over four seasons. He is to make $1.48 million this year.