Manny Pacquiao -- House Hunting In Bev Hills ... Scopes Diddy's Old Digs

Seems Manny Pacquiao may have a plan on how to spend that $100 mil paycheck after all ... 'cause he's been looking at real estate in Bev Hills -- including the BALLER mansion Diddy used to call home.

TMZ Sports has learned ... Manny and his crew went to scope out the 10,000 square foot estate this past weekend and sources say he "really liked" what he saw.

The mansion is insane -- 7 bedrooms, 7.5 baths, home theater system, massive backyard and a SICK mancave with a pretty awesome wet bar.

Diddy used to live in the home back in the day -- and sold it in 2001 for $2.313 million.

The new owners renovated the hell out of the place -- and now it's on the market for a cool $12.5 million ... pocket change to a fat cat like Manny.

Our real estate sources tell us Manny is definitely interested in the house -- but didn't make an immediate offer ... in part because he's got that whole fight thing he's trying to focus on.

But we're told Manny is expected to make a decision whether to pull the trigger or pass in the near future.