Justin Bieber's discarded shoe could land a lucky fan a few thousand bucks ... and there's still another one out there.

Biebs took the Yeezys off his feet and hurled 'em into the crowd during a Sunday night concert in Germany. The lucky dog who nabbed the right sneaker already has it up on eBay ... for a starting bid of 5,000 euros (about $5,670 in U.S. dollars).

The seller claims it's the original, and there are more pics to prove it, if needed. The description also says part of the sale will be donated ... but it's unclear to what.

Bieber's left shoe is also online, but not for profit -- @theleftyeezy has more than 5,000 followers on Instagram. And if you're curious about JB's shoe size, here it is ... allegedly.

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