Will are you SERIOUS. HELL the fuck NO they shouldnt announce this as an injury. You have HBK go down to a worked injury right off the bat, and then merciless destruction By Jericho for the next 5 or 6 minutes. I mean just utter erattication, pure hatred. HBK doesnt look weak (not that it matters if he does) becuase, he is hurt, y'know. And this is unsanctioned, so he is "at jerichos mercy" after the injury happens. SO Jerichio just utterly whipes the floor with him, earning him the last bit of epic heel heat to be the top heel challenger for the belt til HBK comes back...for their WM rematch.
So apparently you didn't see the Chris Jericho "squash" match that he and Shawn Michaels put on at the Great American Bash, to play off the "fake" eye injury.
Why on earth would it be anything "different" to have them once again, twice in a row no less, allow Jericho to completely squash H.B.K.?? Not to mention, that'll hurt H.B.K. in a ways making him look defenseless and too weak to defend the honor of his Wife.
Having the injury announced could thrive Jericho into a riot because he still is without the opportunity to "end" the career of H.B.K. himself. If anything, this is playing in the hands of making this storyline even greater.. with Jericho's insanity slipping away even more.
Jericho is hell bent on being known for ending H.B.K.'s career. So if H.B.K. suddenly can't go due to an injury Jericho didn't give him, it'll send him into a frenzy.
And Frenzy > Second Jericho Squash match over H.B.K.
Easy. this is TOO easy now. As easy to book as it gets. It sets up everything so well. And it would be a huge epic waste to just announce Shawn being hurt and discontinue it.
See above.
If someone punched YOUR wife in the face, would you let it stop you?? No. Its an unsanctioned match. So they cant "stop" him from fighting due to injury. its fricken unsanctioned. Talk about an utter and complete abolishment and destruction of kayfabe.
Again.. you say it like people believe this is REAL. If someone punched my Wife, I'd go after them until I likely couldn't breathe.. but it likely wouldn't be scripted for someone to have punched my Wife, either.
I get the feel for ruining the WHOLE storyline based off an unfortunate event, I do. But I'd rather not see H.B.K. risk even more serious damage in trying to play off storyline.
If H.B.K. goes into this match hurt, and gets hurt worse.. what happens if he really WOULD suffer a career-ending injury? Then your storyline is shot to shit completely. (save for Jericho parading around with what he wanted to do all along.

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Thats about the epitome of it. Calling it off sue to HBK injury is absolutely out of the question, and would ruin all the good that can be done, even if it WAS remotely close to a viable option. which it isnt.
If you really wanna go through with it, then since it's "Unsanctioned" have Lance Cade AND Chris Jericho double team Shawn Michaels from the off-set, before the match ever begins. 5-10 minutes later, H.B.K. is laid out completely. And there is YOUR idea.
OR.. remember that little rumor about Sid Vicious returning? Oh yeah.. perfect set-up situation.
Sid returns as a "friend" of Shawn Michaels, and replaces him. Jericho can still play off Shawn being too scared to face him because of Shawn's "eye" injury.. and Sid can be brought back in a decent feud, in a great way.