NFL castaway Jeremy Shockey -- who once signed a $26 million contract with the Giants -- is now locked in a legal battle with a Miami landlord ... over $16,000 ... TMZ has learned.
Shockey filed a lawsuit against the landlord of a $14,000-a-month Miami beach mansion -- where he lived for ONE MONTH last summer -- claiming she's holding his security deposit hostage for no good reason.
Shockey claims he paid the landlord one month's rent, plus a substantial security deposit ... but when he moved out, she refused to return $16,000 he's owed.
Shockey claims he left the place in perfectly acceptable condition ... so the landlord's got no leg to stand on. Now, he's suing for $16,000 plus interest.
Calls to the landlord weren't returned.