Rocker doesn't project to make the Rangers rotation if the five starters ahead of him are healthy, Kennedi Landry of MLB.com reports.
The Rangers optioned Rocker to Triple-A Round Rock on Friday.
Rocker (0-2) took the loss Thursday against the Athletics, allowing three runs on seven hits and no walks across 4.2 innings. He struck out two.
Rocker is expected to make another start for the Rangers during the final week of the season, Evan Grant of The Dallas Morning News reports.
Rocker did not factor into the decision in a win over Seattle on Thursday, allowing one run on three hits and two walks over four innings while striking out seven.
The Rangers selected Rocker's contract from Triple-A Round Rock on Thursday.
Rocker will be called up from Triple-A Round Rock to make his major-league debut Thursday in Seattle, Shawn McFarland of The Dallas Morning News reports.
Rangers general manager Chris Young on Sunday said the team has not ruled out the possibility of Rocker making his major-league debut before the end of this season, Evan Grant of the Dallas Morning News reports.
Rocker struck out 10 while allowing one hit and zero walks over five scoreless innings Wednesday for Triple-A Round Rock.
Rangers general manager Chris Young confirmed Thursday that Rocker will be promoted from Double-A Frisco to make his next start with Triple-A Round Rock, Evan Grant of The Dallas Morning News reports.