With little recognizable but an eye and chin, the man who lost most of his face in a vicious attack by a raving naked man on a Miami causeway is up against daunting medical challenges, including the possibility of infection delivered through human bites.

For now, Ronald Poppo, who has lived half his life on Miami’s streets, is without his most basic features.

“The loss of the face is one of the most devastating injuries because in so many ways it defines our identity,’’ said plastic surgeon Chad Perlyn, an assistant professor in the surgery department at Florida International University’s Herbert Wertheim College of Medicine. “He has a long road back, both physically and psychologically.’’

In a random encounter, Poppo, 65, was assaulted on the busy MacArthur Causeway over the Memorial Day weekend. As cars zoomed by, his attacker, Rudy Eugene, chewed off chunks of Poppo’s face in what police suspect was a drug-fueled rage. Detailed online photos of what is purported to be Poppo’s face show the left eye gouged out and the other features — eyelids, nose and lips — gone. Police have reported Poppo to be in critical condition. The Ryder Trauma Center at Jackson Memorial Hospital will not confirm his condition or release any personal information until they receive consent from a family member or surrogate.

But a police union representative for the officer who stopped the attack described the devastation to Poppo’s face. “He had his face eaten down to his goatee. The forehead was just bone,” Sgt. Armando Aguilar, president of the Miami Fraternal Order of Police, told the Associated Press. “No nose, no mouth.”

Poppo’s recovery will take months, possibly years, of medical and psychological treatment in a costly and ambitious effort to rebuild the features on his face or, possibly, replace it altogether in a transplant that has only been performed about two dozen times in the world. One of the most recent procedures, performed in March, was led by a Miami-born doctor, Eduardo Rodriguez.

“The human mouth has one of the highest counts of bacteria, and with bites where the skin is punctured, the teeth and saliva carry the bacteria into the wound,’’ said Perlyn, part of the Miami Children’s Hospital plastic surgery team. “The key to his injuries beyond the infections is determining how much tissue damage or loss there is. Damaged tissue can be repaired, but where there is loss, the feature must be reconstructed.”

Though few details are available about Poppo’s condition, several plastic surgeons and experts — none treating the patient but experienced in facial reconstruction — say that doctors treating a patient with such extensive injuries would confront steep challenges to construct a semblance of a normal face.

“Based on the extent of his injuries, he has a really tough road ahead. Facial reconstruction is difficult in the most simplistic case of trying to restore a feature back to the exact form and function,” says Dr. Reza Jarrahy, the co-surgical director of the University of California at Los Angeles Health Systems’ newly launched Face Transplantation program. “And prior to just a few years ago, the idea of a face transplant was far-fetched, a Hollywood type notion.’’