TMZ Sports has learned ... Allin suffered the injury less than two minutes into his match against "Switchblade" Jay White at AEW Dynamite on Wednesday ... when he attempted a front flip off the top rope.

It goes without saying his landing didn't play out like it was supposed to ... and he made awkward contact with the floor, which caused his dog to snap.

Allin was clearly bothered ... and briefly held his foot before limping back up.

Instead of calling it a night, the badass highflyer proceeded to wrestle in his first-ever match against White for 10 more minutes ... continuing to jump off the top rope and going about his business.

Ultimately he was pinned after running into a Blade Runner from White.

The ironic part -- during the match, Allin had his ankle "broken" at the hands of Bullet Club Gold so he could have enough time away from the squared-circle to tackle Everest.

Of course, Allin was already pretty beat up -- he shredded his back after flipping off a ladder and falling through glass in his retirement match with Sting.

Allin previously told us how stoked he was to make the Mt. Everest climb -- despite not having a ton of experience (he only trained six months), he was given the green light to do it.

Now he'll be sidelined for a bit ... but is making the most of it -- he tells us Tony Hawk is planning to do a trick off his cast next week for charity!!