"Mike understands that when you're up here, you need to get outs," Roberts said. "To send him back out there and work through some things, go back to getting guys out, hopefully we'll see him later."
Frias will work as a reliever with Los Angeles, giving the team a nine-man bullpen for Sunday. It's a setup that is expected to last only for a day, as outfielder Yasiel Puig (hamstring) will be activated from the DL on Monday, but Roberts didn't want to make that commitment.
"We'll see how it goes. Carlos is here certainly for today," Roberts said. "We expect Kenta [Maeda] to go out there and throw well. A nine-man bullpen is unconventional, obviously. After today's game, we'll see where we're at and make the decision then."
Puig had the day off Sunday at his rehab assignment with Class A Advanced Rancho Cucamonga. In five games with the Quakes, Puig has gone 5-for-12 with a homer and three walks.
The exit of Bolsinger puts the Dodgers rotation after the current homestand further into a state of flux, as Julio Urias is expected to be taken out of the rotation following Wednesday's start against the Nationals in order to limit the teenager's innings. Frankie Montas was the only Minor Leaguer mentioned as a possibility to replace Urias, but the rotation of Triple-A Oklahoma City presents several options.
Any replacements will likely be short term, as both Brandon McCarthy (elbow) and Hyun-Jin Ryu (shoulder) are working through rehab assignments and on track to return in July.
The Dodgers also don't need a fifth starter until June 28, thanks to an off-day Thursday, but the team has not yet decided if it will skip the fifth starter's spot.
McCarthy will make his next rehab start Wednesday for either Rancho, the team he is currently with, or OKC, throwing four innings or 45-50 pitches. Ryu will pitch five innings or 65 pitches on Thursday or Friday.
While Ryu's last start with Rancho went well with five strikeouts in four scoreless innings, Roberts reported the average velocity from the start to be 86 mph with fastballs reaching as low as 82 mph. Roberts said an average of 88 mph would be needed to pitch in a Major League game, an improvement he expects Ryu to make.
Alex Wood (triceps) could also make a return in July, but no plans for a rehab assignment have been announced.