In case you missed it ... Lacy was heavily criticized for appearing larger than usual when he arrived to camp to kick off the 2015 season ... and never seemed to drop the excess weight.
McCarthy says Lacy needs to get his ass in shape for next season ... or else.
Enter fitness mega-mogul Tony Horton -- creator of the world famous P90X program -- who says he would LOVE the opportunity to PERSONALLY train Lacy this off-season ... because he's confident he get real results.
Horton tells us he's already got a 3-month bootcamp style plan in mind -- which would get Lacy back into top form.
"Time is ticking ... so it's time for him to step up."
BTW, a bunch of NFL stars have raved about P90X -- including Ray Lewis.