Burnes was called up from Triple-A San Antonio on Wednesday, Adam McCalvy of MLB.com reports.
Wednesday's scheduled starter, Chase Anderson, was a late scratch due to a finger laceration, and apparently the Brewers placed him on the injured list before the game and recalled Burnes, though no announcement was made until after first pitch. According to Tom Haudricourt of the Milwaukee Journal Sentinel, Burnes was originally scheduled to be activated for Thursday's game, but the team received approval for the last-minute roster move.