Fantasy Football nerds, listen up ... Jake Plummer says he's expecting a monster year from Justin Herbert -- telling TMZ Sports he thinks Jim Harbaugh will get the very best out of the Chargers star.
Plummer played in the NFL at the same time as Harbaugh in the late 1990s -- and it's clear as day he grew a ton of respect for the Bolts' head man. So much so, he believes Herbert's game will soar to new heights under his tutelage.
The former Arizona State star quarterback says because Harbaugh wasn't the most athletic signal-caller, he grew a massive football IQ ... and he anticipates that being passed on easily to Herbert.
Plummer said one of Harbaugh's most recent hires -- offensive assistant Marc Trestman -- should also play a role in Herbert's development ... explaining to us the longtime coach will get the 26-year-old really ready to shred defenses.
Of course, Plummer was already high on Herbert's game before the hires -- but he told us with the two guys on the Chargers' staff, "Maybe we haven't seen the best of him yet!"
Plummer also spoke to us about this year's crop of NFL draft quarterback prospects ... and he -- like everyone else -- says Caleb Williams should be the No. 1 overall choice.
But, he said he really likes what he's seen from two others as well -- Bo Nix, and, you guessed it, Harbaugh's former Univ. of Michigan QB, J.J. McCarthy.