Manager Don Mattingly hasn't confirmed that Ryu won't start in Colorado, but essentially did Sunday when he said that Frias is "working toward" the Wednesday night start and won't be used out of the bullpen "unless we get news that Hyun-Jin can pitch, and that's not likely."
Frias threw six scoreless innings in his lone spot start against Washington on Sept. 3.
Ryu's MRI on Monday will determine when, or if, he can return this season. He complained about stiffness and soreness in the back of the shoulder Friday.
Although the Dodgers have 17 active pitchers (including Ryu), Mattingly said general manager Ned Colletti is considering calling up one more, but he would not provide a name.
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.