Chris Paul -- Clippers Star Buying Bel Air MANSION from Avril Lavigne

Los Angeles Clippers star Chris Paul is planning to stay in town a while ... 'cause he's about to drop $8.5 MILLION on a sick Bel Air mansion that he's buying from Avril Lavigne ... TMZ has learned.

Sources tell us ... Paul fell in love with the 12,184 square foot place, which Avril originally listed for $9.5 mil and decided he had to make a move.

The mansion -- located in a hoity-toity private community called Bel Air Crest -- includes 8 bedrooms and 10.5 bathrooms, a wine cellar, 10-car garage, gym, sauna and a covered outdoor living room.

We're told the real estate agents who engineered the deal are Jade Mills and Zach Quittman from Coldwell Banker in Beverly Hills who reps Avril, and, Ikem Chukumerije from SportsRelocation.com, who reps Chris.

Before Avril moved in ... Travis Barker lived in the place with his ex Shanna Moakler ... and it was even featured on their MTV reality show "Meet the Barkers."