Infantry Veteran

• WWizards of the Coast2010-08-15
  Official Ruling
  An “attacking creature” is one that has been declared as an attacker this combat, or one that was put onto the battlefield attacking this combat. Unless that creature leaves combat, it continues to be an attacking creature through the end of combat step, even if the player it was attacking has left the game, or the planeswalker it was attacking has left combat.

Rulings via Scryfall