Frontline Rebel

• WWizards of the Coast2017-02-09
  Official Ruling
  If, during your declare attackers step, Frontline Rebel is tapped or is affected by a spell or ability that says it can’t attack, then it doesn’t attack. If there’s a cost associated with having it attack, you aren’t forced to pay that cost, so it doesn’t have to attack in that case either.

Rulings via Scryfall