NFL on Fox Mansion Wasn't David Beckham's

Beckham appeared in a comedy sketch with the new "NFL on Fox" comedy guy Rob Riggle ... and in the sketch, Rob joked that he broke into "some football player's home" to throw a raging party. Enter the punchline when Dave said the house was his. Funny stuff.

The home was gigantic ... and SOOO gaudy ... with a massive pool .. a fancy dining room decked out in gold ... and a tacky master bedroom.

But sources close to Beckham tell us ... the footage was NOT shot in Dave's real-life Beverly Hills mansion ... but rather a rented out home made to look like Casa de Becks.