"If I could do it all over again, when that coach came to me and told me, 'You should switch your position to receiver or cornerback,' I would have did it."
That's Chris Johnson -- one of the best running backs that's EVER lived -- telling TMZ Sports he's so upset with the way the NFL's treated RBs over the last decade ... he wishes he had never played the position.
Of course, today's NFL tailbacks are learning that the hard way ... stars like Le'Veon Bell, Melvin Gordon and Ezekiel Elliott are either having to miss games or threaten to miss games to get a somewhat fair contract.