Lopez was called up from Double-A Biloxi on Thursday.
With Chase Anderson (oblique) headed to the disabled list, Lopez was promoted to the Brewers to offer an extra arm out of the bullpen while the team figures out who will replace Anderson in the rotation. The 24-year-old was recently shifted to a bullpen role after struggling as a starter for the Shuckers, and he has posted three scoreless innings of relief since making the move.