Besieged by injuries and COVID-19 cases in their playing group, the Sixers made a third appeal for Smith to be able to play in Friday night's final against the Perth Scorchers.
However, AAP has been told that was knocked back late on Thursday, with Smith no longer on stand by for the clash and the Sixers having since moved on.
It's believed officials determined that there was adequate batting cover available for the Sixers in the local replacement pool, despite them being without three players through COVID and up to another two through injury.
Josh Philippe, Mickey Edwards and Jack Edwards are all infected by coronavirus while Jordan Silk has been ruled out of the final with a hamstring injury.
Daniel Hughes will need to pass a pre-match fitness test on his ankle to play, after missing Wednesday's win over the Adelaide Striker due to injury.
Captain Moises Henriques and retiring veteran Stephen O'Keefe will both play through calf injuries in the decider, after being declared fit to play.
It means the Sixers will again use a member of the player replacement pool and assistant coach Jay Lenton behind the stumps.
Fellow pool member Jake Carder will play in the final, while a third replacement from the pool in Nick Bertus will also come into the side for Silk if Hughes is unavailable.
The Sixers had made an application to contract Smith before the finals last week, when he suddenly became available with the New Zealand ODI series postponed.
However, that was dismissed by Cricket Australia and the clubs, after it was agreed mid-season new players could only come from the replacement pool set to deal with COVID-19 outbreaks.
A fresh request was made before the Sixers' clash with Adelaide when Philippe contracted COVID-19 and Hughes was injured, but it was again knocked back.
The spate of injuries from the mid-week match had then prompted a third bid, before its denial on Thursday spelled the end of any hopes of Smith playing.
Several Sixers players have voiced their frustration on the issue, with Dan Christian posting a tongue-in-cheek tweet on Thursday asking if anyone could fill in for the club as long as they weren't a Test player.
Henriques admitted he was "clueless" about the situation on Thursday, while Perth captain Ashton Turner claimed he would have liked for Smith to play.
Friday's final will be contested on neutral ground at Marvel Stadium and across-town from Australian Open tennis, with Perth unable to host the BBL game in Western Australia.
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