The Royals outrighted Rosario to their alternate training site Sunday.
Rosario was designated for assignment by the Royals on Thursday.
Rosario (arm) was activated from the 10-day injured list Friday, Alec Lewis of The Athletic reports.
Rosario (arm) was placed on the 10-day IL on Thursday, Jeffrey Flanagan of MLB.com reports.
Rosario won't begin the regular season on the 30-man roster while dealing with arm tightness, Lynn Worthy of The Kansas City Star reports.
Rosario had edged into the lead for the final spot in the Royals' bullpen when camp was suspended, Jeffrey Flanagan of MLB.com reports.
Rosario was claimed off waivers by the Royals on Thursday, Jeffrey Flanagan of MLB.com reports.
Rosario was designated for assignment by the Cubs on Monday, Jesse Rogers of ESPN.com reports.
Rosario was optioned to Triple-A Iowa on Friday.
Rosario (1-0) retired the lone batter he faced and earned the win in Friday's game against the Pirates.