Matt Ryerson-USA TODAY Sports

Spinal and orthopedic surgeon Dr. Johnny Benjamin is a big mixed martial arts fan who consistently gives his feedback on controversial medical issues such as concussions, testosterone replacement therapy and drug testing.

In a recent interview with Bloody Elbow's Steph Daniels, Benjamin named a couple fighters whom he felt should retire.

The most surprising name he mentioned was Stefan Struve, who boasts a 25-6 mixed martial arts record and is currently ranked the No. 10 heavyweight in the UFC's official rankings.

"How many times has he been knocked out? I know he's a young man, but he's been knocked out more than a few times ... At some point, someone really needs to ask the question, should he still be fighting? That many concussions, so quickly, and at this young age ... a person has two types of age, chronological and physiologic age. Stefan's license may say he's 25, but in physiologic years, he's much, much older than that, with all the concussive force that he's sustained ... I'm sure nobody will like to hear this, but Stefan Struve really needs to think about retiring."

While the "Skyscraper" is a tough opponent for anyone at heavyweight, five of his six losses have come by way of (technical) knockout and the majority of those have been undeniably pretty brutal.

Look no further than his most recent KO loss to Mark Hunt at UFC on FUEL 8 earlier this month, where Struve suffered a broken jaw, to see the type of knockouts the young fighter has suffered in his career.

Despite his tendency for coming up short against strikers with serious power, few pundits have called for Struve's retirement, after all, he just turned 25 years old last month.

Nevertheless, Benjamin said that the damage the brain suffers each time a concussion is sustained is enough reason for the Dutchman to consider hanging the gloves up.

"If it's not him that will make that decision, then Dana White needs to start talking to him about retiring. The question out there is how many sustained concussions is too many, and according to the latest literature that's coming out, the answer is starting to look like it's somewhere between two and three. That's where you start having permanent changes."

Additionally, despite looking impressive in a knockout victory over Brian Stann at UFC on FUEL 8, Benjamin also believes that PRIDE legend Wanderlei Silva should call it a career after 49 professional fights.

Like Struve, he believes "The Axe Murderer" has suffered too many (six) brutal knockouts throughout the course of his long career, which could lead to permanent side effects.

Does Benjamin bring up a legitimate new concern in the sport of mixed martial arts here?