It's true ... at least, that's according to the ex-NFL star, who tells TMZ Sports he's slated to be on the microphone when it comes time to belt out the national anthem before the big game's kickoff.

The former Patriots tight end, though, said it won't be a solo act ... explaining to us the New Directions Veterans Choir will be there to help him get through it.

"It's kind of like I'm the quarterback," Gronkowski said, "and I have the best offensive line in front of me so they can make me look good."

Gronk says he'll certainly be in need of the assistance ... telling us that when he performed the song recently for the bowl game's committee -- which included his good pal Julian Edelman -- it was met with some rotten reviews.

"I got to keep practicing," he admitted.

Outside of Gronkowski's vocals, the game -- which will pit UCLA against Boise State at SoFi Stadium on Dec. 16 -- will feature a whole lot of other fun activities ... including a dance cam and a special Gronk-themed drink.

As for why the future Hall of Famer will be so prominently displayed during the college football matchup ... he's actually the game's host -- explaining to us that he took the role from Jimmy Kimmel after he found out the LA Bowl (formerly the Las Vegas Bowl) was the final game he played in when he was a student-athlete at U of A.