A suspect in Oklahoma City should've let sleeping dogs lie ... because he's almost certainly nursing a sore leg -- and facing an extra charge -- after dragging a K9 unit with his truck in a shocking video.

Dramatic footage shows cops performing a traffic stop that goes from routine to chaotic in seconds ... when a suspect standing out his box truck suddenly makes a break for it.

The K9 unit -- named Dash -- runs after the guy as he runs to truck, opens the door and gets behind the wheel ... latching onto the guy's leg with his jaws as the man starts to drive away.

The officers run over too, and they try to pull Dash off, but he's like a dog with a bone -- in this case, the bone is this dude's femur -- and he won't let go as the truck drives down the road.

Another angle shows Dash being dragged a long distance ... before cops say he eventually fell off and narrowly avoided being run over.

The suspect, Jose Balderas, was later taken into custody by police. Local outlet KOKH says he was arrested on complaints of mistreating a police dog in the commission of a crime, unauthorized use of a vehicle after a felony conviction, eluding a police officer and interfering with an officer.

Cops say Dash will take a few weeks off while he recovers from road rash.

Good boy, Dash!