Fighting with a stunned creature directly un-stuns it, it is not a separate use action. I agree that there would need to be a creature for it to fight, or you could not perform the 'Fight' usage.
I used to thing the same thing you did. That you could only un-stun a creature if you have the option to 'Use' the creature. If the creature is stunned and is explicitly told to fight (anger, Gauntlet of command, etc...) that it would not un-stun as it was expressly given the option to fight. Though if it were a member of the called house, it would ready as Debiant said, and then you could un-stun it as a separate use.
It came up at a PAX tournament and the judge ruled that fighting with a stunned creature directly un-stuns and exhausts it. Cited rules reference page 7:
When a player uses a creature, that player must exhaust the creature, and the player has the option to reap, fight, or to trigger the creature’s “Action:” ability.
Any ready creature of the active house may reap. When a creature is used to reap, its controller gains 1 Æmber for their Æmber pool. Then, all “Reap:” abilities the creature has, if it has any, resolve.
Any ready creature of the active house may fight. When a creature is used to fight, its controller chooses one eligible creature controlled by the opponent as the target of the attack. Each of the two creatures deals an amount of damage equal to its power (the value to the left of the card’s title) to the other creature. All of this damage is dealt simultaneously. After the fight resolves, if the creature that is being used to fight survives, all “Fight:” abilities the creature has, if it has any, resolve.
A creature cannot fight if there is no enemy creature that can be chosen as the target of the attack.
Any ready creature of the active house may trigger its “Action:” ability, if it has one. When a creature is used to trigger its “Action:” ability, the creature exhausts and all “Action:” abilities the creature has resolve."
Note that 'un-stun' is not a 'USE' option. Only 'Fight', Reap' and 'Action'
second citation, Page 12:
STUN, STUN STATUS CARD
When a creature becomes stunned, place a stun status card on it. The next time the creature is used, the only thing that happens is the creature exhausts and the stun card is removed. It does not reap or fight, and any
“Reap:,” “Fight:,” or “Action:” abilities on the creature do not resolve. Constant abilities and abilities that do not require the creature to reap, fight, or be used are still active. If a stunned creature is attacked, it still deals damage to the attacking creature during the fight. While a creature is stunned, it cannot become stunned again.
Since we know that using a creature encompasses 'Fight' 'Reap' and 'Action' and that using a stunned creature un-stuns it. We can say that if a creature is able to perform any of those three 'use' actions, any of them will remove the stun effect.
I suspect you are confusing it with the ruling for Wild Wormhole...where if you play Wild Wormhole and have no cards in your deck, you do NOT shuffle and draw, because you don't draw the card then play it, you just play it.
Nothing in the rules suggests that other effects/triggers/mechancis can't be executed mid-effect. In fact, the FAQ entry about Wild Wormhole shows that effects can trigger and resolve while another effect is resolving.
The Discard Pile glossary entry in the rulebook says: "When a player runs out of cards in their deck and are required to draw, they shuffle their discard pile to create a new deck."
You do it when you need to draw and there are no cards in your deck.
The effects of "sergeant Zakiel" would ready the target "creature" It would not remove the "stun" as "sergeant Zakiel" Play action does not state that it does. Therefor the target creature would be readied if it was exhausted but it would not be able to fight as it is still stunned.
Not to belabor the point, but just to leave this as a reference in case other people search this for answers.
The relevant information on this correct answer comes from the full rulebook, "Glossary" under "Stun, Stun Status Card". The following is the pertinent excerpt.
So any time you "use" the creature, even in response to a card telling you to execute one of the ways to "use" the creature, it will simply remove the "stun" effect without actually executing that use.