Mercy Miller -- rap legend Master P's son -- is gearing up for his second season at Houston ... and Cougars legend Otis Birdsong is expecting BIG things from the sophomore -- telling TMZ Sports, "He's already something special."
We caught up with the former All-American out at LAX ... and he explained Mercy paid his dues absorbing information from head coach Kelvin Sampson last year, and is now better because of it.
"In coach Sampson's system and culture, you got to wait your turn," he said.