If there are Units present at the Battlefield the Combat is taking place at, but do not have a designation, they gain the same designation as their Controller now
§ 323.2.a Core Rules PDF (officieel)
§ 323 When a Cleanup occurs, the following Tasks become Outstanding in the order described:
§ 323.2 2. Assign or Remove the Attacker or Defender designation from Units as needed if there is a Combat in progress
