Steve Nash -- Drops $4.8 Million ... On Retirement Home

Forget Shady Pines, when Steve Nash retires ... he'll be in the lap of luxury -- 'cause the L.A. Lakers star just dropped $4.8 million on a Manhattan Beach pad ... TMZ Sports has learned.

Our real estate sources tell us ... Nash had been on the hunt for a permanent home on the West Coast -- somewhere he could settle down after his NBA career. Then he found a 4,175 square foot gem just 2 blocks from the sand.

Problem is ... it's super ugly and outdated.

Solution is ... we're told Nash is gonna knock the whole thing down and build his dream house.

We're told the place was originally listed for $5 million ... but Nash was able to get the price down to $4.8 mil with an all-cash offer. Strong.

Sources tell us Nash already has a builder in mind and wants to get to work ASAP.