King is slated to serve as the Marlins' opener for Sunday's game against the Mets, Christina De Nicola of MLB.com reports.
Janson Junk had been set to start Sunday but was a late scratch before being placed on the 15-day injured list due to a right shin injury. King will make his first MLB start in what will be a bullpen day for Miami. The southpaw hasn't recorded more than four outs or thrown more than 20 pitches in any appearance this season, so he shouldn't be expected to work more than an inning or two.