While everyone is worrying about Regnifo, Perkins, and Ortiz and rightfully so it feels like Frelick is being overlooked. If you take Regnifo and Ortiz out of the equation, Frelick has arguably been the Brewers worst regular this season. Put it this way Frelick is worse than Hamilton so far this season.
Right now, he owns a slash line of .222/.292/.304 with a 70 wRC+ and -0.2 WAR. Over at FanGraphs, he has been a negative contributor both offensively and defensively, so he is not really providing much value on either side of the ball.
That said, his splits against right-handed pitching are actually respectable, so maybe the answer is giving him a platoon partner against lefties.
Frelick's splits:
VS LHP: .120/.182/.200 for a wRC+ of 8. That is not a mistake that is his wRC+ against LHP.
VS RHP: .269/.341/.352 for a wRC+ of 99.
Mitchell is currently being sat against LHP but I believe the Brewers also need to sit Frelick against LHP. The Brewers definitely need another RH batter in the OF as neither Mitchell or Frelick should be seeing LHP going forward and no Frelick seeing a lot of pitches is not a positive when he does absolutely nothing after seeing all those pitches.
Frelick's statcast info: