Caleb Williams Gets USC Jersey Retired, Snoop Dogg & John Legend Send Congrats

Caleb Williams hasn't made his mark on the NFL just yet ... but his college legacy is cemented forever -- as USC announced he's getting his No. 13 jersey retired!!

The school made the move official on Tuesday ... and evoked the help of some Hollywood celebrities for the big moment.

John Legend , Snoop Dogg and more joined in to congratulate Williams on his accomplishment. Some of his former USC team members -- including head coach Lincoln Riley and quarterback Miller Moss -- also gave Williams his flowers in the tribute video.

Legend even sang a bit of his hit song, "Ordinary People," for Caleb ... a nod to the not-so-great rendition he gave during the Chicago Bears' rookie showcase -- which was captured on "Hard Knocks" cameras.

The rap legend also cracked a joke about Williams' performance ... saying he should leave all the singing to "Uncle Snoop."

It's no surprise why USC is hanging his jersey up -- in his two years with the program, he completed 599 passes for 8,170 yards and 72 touchdowns ... and it's tradition for Southern Cal to retire the digits for all Heisman winners.

Speaking of, Reggie Bush -- who recently has his Heisman trophy win reinstated -- is getting his No. 5 jersey enshrined as well.

Congrats to Caleb and Reggie!!!