Can I use the exhaust ability of a unit in combat?

The cost of using an ability with the exhaust symbol is to exhaust that unit. If you just moved a unit into combat using the standard move, then you already exhausted the unit as the cost to do that, so you wonʼt be able to use its ability with the exhaust symbol that same turn. If the unit is defending, it might be ready and then you can use abilities that require exhausting it in combat (as long as those abilities have the Action or Reaction keyword).

Related: Rule 308.1.a, Rule 806.1.c.2