Shaq came out firing after Damian went on "The Joe Budden Podcast" and questioned the NBA legend's rap skills ... and the diss track proves the big man still has bars.

The basketball Hall of Famer pulls out all the stops in his rap comeback, calling Dame a worse player than Trevor Ariza ... and saying the Portland Trail Blazers point guard can't hold a flame to real MVP candidates like Steph Curry and Russell Westbrook.

In case you missed it ... Damian, who considers himself a pretty good rapper, started the beef last week when he told Joe Budden, "I think I rap better than Shaq."

Dame's shade didn't stop there, he also took a big fat dump all over Shaq's rap career from the '90s ... saying, "People weren't looking at it like it's a real rapper. It was like, 'that's Shaq rapping.'"

Shaq didn't take Dame's criticism kindly ... and now we're waiting for Damian to fire back with a diss track of his own.