John Elway made a desperate move trading for Joe Flacco ... and it could end up being a HUGE mistake -- so says Elvis Dumervil, who tells TMZ Sports, "Flacco is no Peyton Manning."
Elway took a page out of his 2012 Broncos playbook Wednesday ... acquiring a veteran Super Bowl MVP with the hopes of revitalizing a tired Denver franchise.
The problem? Elvis says Flacco ain't even close to what Manning was when Denver picked him up 7 years ago ... and now the former Bronco is SERIOUSLY concerned for the team's GM.
"It's a big gamble. Definitely desperate, no doubt ... It can be a great deal, or it can be another bad decision by John Elway."
Elvis' biggest issue with the move is Flacco's skill set -- the pass rusher tells us Joe NEEDS a good OC to thrive ... and he's worried that ain't there in Denver.
In fact, Dumervil says if Flacco DOESN'T have an elite play caller ... things are gonna get ugly at Mile High quickly -- the exact opposite of what went down after Elway signed Manning.
"[Elway] did a genius move with Peyton Manning. But unfortunately, Joe Flacco is no Peyton Manning."
On the other side of things, Dumervil -- who also played for the Ravens -- says Baltimore is the clear winner in the trade ... telling us the move will only help Lamar Jackson grow.