NFL Star Clay Matthews -- I'm Moving Into Justin Bieber's Hood

Green Bay Packers linebacker Clay Matthews is thiiiiis close to having Justin Bieber as a neighbor ... 'cause he bought land in Bieb's Calabasas community -- but the singer could be OUT by the time Clay's home gets built.

TMZ Sports has learned ... Matthews recently dropped $2.6 million on a plot of undeveloped land in The Oaks ... a gated community littered with huge stars like Bieber, Travis Barker, Keyshawn Johnson, Nikki Sixx and (coming soon) Kourtney Kardashian.

Matthews -- who signed a $66 million contract extension last year -- is planning to build his dream home on the property ... but we're told construction has not started yet.

And with Justin Bieber telling people he's planning to leave The Oaks, it's very possible Calabasas could be Bieber-free by the time Clay is ready to move in.

And get this ... Clay scored a huge deal on the property -- it was originally on the market for $4.4 mil. We're not sure if the drastic price cut is due to the fact it's located near Bieber's home, but it's very possible Bieb was a factor.