Is Jimmy Garoppolo gonna be the next big thing for the 49ers?

YUP.

Like, as big as Joe Montana or Steve Young??

YUP.

That's E-40 -- a HUGE 49ers fan -- weighing in on the hottest QB in football ... after Garoppolo crushed it in his first 3 starts for SF.

We got the Bay Area rap legend out at Kendrick Lamar's charity concert in L.A. ... and while he didn't say too much, it was clear he was all about Jimmy G.

"That boy gonna be one of them ones," E-40 told TMZ Sports.

Believe it, people -- he's basically an expert on QBs ...