OUCHIE!!!
Wow, blindboy, that's horrible sounding! I know nerve damage, as my entire sciatic nerve was stretched from the bottom of my spine literally down into my big toe back in 2001 when I had a 3-level global lumbar fusion (that was a real OUCHIE!!) and the nerve DOES grow back (even though mine wasn't severed) but it heals slowly - about an inch a year, so it's a lot better for me in the higher areas, but the foot and toe area still burn and hurt at times, and sometimes I feel like I've got a rock in my shoe, when there is really not anything at all in there that shouldn't be.
But again, mine was stretched, and over a really long distance, so it will be a different healing and kind of pain in your case. Probably it will hurt more at first (especially when the numbness starts to go away and is replaced with sensation...it will likely be a rather painful sensation.. BUT on the really positive side, there is only a really small length of nerve to heal, so it won't be as slow as mine (I hope!).
But you probably will need painkillers to play tomorrow, unless you can somehow make sure you NEVER forget and try and use that finger, which in such a short period of time is unlikely... and as others have said, you do not want to keep aggravating it by over-using it when it should be treated as gently as possible, Can you put something on it (even a rubber thing or something that would get in the way and would physically prevent you from forgetting and by force of habit, hitting the string with that finger? As the slide worked before for you, and you also had a real good reason to get real good at slide guitar!
having something on or wrapped around that finger - even just gauze or tape or anything to prevent contact without a good amount of padding in between - would help a lot in preventing further injury and and also helping you more quickly to get in the habit of NOT using that finger to play.
I hope this helped somewhat, and was not depressing, I know you can't stop playing for any length of time, and especially so in a band that's gigging, so as with Django and Les Paul (who for years had terribly arthritic fingers on his fretting hand and only - like Django in a way - had real use of only 2 fingers on that hand to do all his fretting with (and any anti-arthritic meds would mess up his stomach and he felt he could not take any of them).
So the last years Les played and fretted with only two fingers for almost all his solo lines (which I say that way, because watching him from up close at one of his Monday night shows at the Iridium jazz club in NYC during his last few years, he did seem able to do some barring with the other fingers for chordal sections of his playing * )
I hope your gig goes great, and your finger heals quickly!
Jim (S)
* although his action was set up especially for him by his sound engineer, luthier, chauffeur, and do-everything-man to Les for over 20 years T.W. (Tom) Doyle,
[who the bass player in my band just happened to move in next door to, and we all most fortunately got to become friends with Tom, which got us extra good access to Les (not very easy, especially as Les' bad moods got worse as he got older and playing was harder for him - but he NEVER showed it on stage - but he WOULD cancel seeing fans after the show and signing their guitars on bad nights - so Tom told us when was good/bad and also got my LP Guitar and photo with Les signed by him on a "good mood" day]
which may have made playing like that possible for Les. (sorry for the inevitable digression that always come with my posts!
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