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Aldon Smith has cleaned himself up and is laser-focused on getting back in the NFL, so says Jay Glazer who tells TMZ Sports ... the former All-Pro deserves a 2nd chance.

The 30-year-old defensive end was a MONSTER in the league before substance abuse issues and domestic violence allegations derailed his career.

But, Glazer says Smith had an epiphany -- and made a life choice to turn his life around, starting with joining Jay's Unbreakable gym in West Hollywood.

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"Aldon's great because Aldon's been working out with our [military veterans] in our MVP program every single Wednesday night," Jay said.

"Aldon has been sober for a while and he's been helping a lot of our vets with their sobriety."

Smith - who hasn't played a down in the NFL since 2015 -- is now trying to show NFL teams he deserves another shot in the league ... and Glazer believes he's earning it.

"We've given a lot of guys second chances. He deserves it as much as anybody I've been around," Jay told us at his GlazerPalooza event at Prestige Imports Miami, where a bunch of SICK exotic cars were on display!

The event benefits Jay's MVP charity which helps military vets and athletes who are dealing with mental health issues.

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Jay says Aldon -- who set the 49ers franchise single-season sack record in 2012 (19.5 sacks) -- is currently at a solid 285 lbs and SHREDDED.

"He is a freak if nature."