"He hated that people loved me more than him," FredEx says.

Of course, Freddie played with D-Mac for 4 seasons from 2001 to 2004 in Philly ... and while it might have seemed like the guys got along back then -- Freddie tells us that ain't the case.

Mitchell says McNabb was jealous of anybody who got more shine than him on the Eagles -- so much so, Mitchell says the QB straight-up refused to throw him the ball!!

In fact, Freddie tells us he thinks Donovan cost him and his family between $20 and $40 MILLION because of his antics ... saying, "It cost me a second contract, you know?"

Freddie is just the latest Eagle to come clean with his hatred toward the legendary Philly QB ... All-Pro right tackle Lane Johnson just called him a snake a few days ago.

And why? It all stems from McNabb saying Carson Wentz should be benched if he can't lead the Eagles past the second round of the playoffs.

For his part, Donovan doesn't seem bothered by the all the talk ... he posted a "Winning!" GIF on Twitter on Sunday night with a caption saying, "Deal with it."

Man ... we've come a long way from 4th-and-26.