If Jake Plummer were on the clock in the NFL draft and needed a QB ... he tells TMZ Sports he'd go with Justin Herbert over Tua Tagovailoa -- and says it's actually an easy choice.

"I would steer away from any damaged goods," the former NFL QB says.

Tua has battled SEVERAL key injuries in his 3-year Bama career ... most notably suffering a dislocated hip last November -- and Plummer says those are just too many red flags for him.

"I would be leery about injuries he's sustained already," Jake says of Tua. "They're not like a broken hand, or a sprained wrist, or something pretty similar. He's working with hips and he's had some problems with his knees, I believe."