The most alarming possibility surrounding Kerby Joseph’s injured knee has now been said out loud.
Dr. Jimmy Liao, a physician and Detroit Lions fan who provides public injury analysis, believes Joseph may need to consider retiring from the NFL to protect his long-term health. It is a sobering opinion involving one of Detroit’s most talented defensive players, but the distinction here is critical: Liao has not examined Joseph’s knee, treated him or reviewed the complete medical information available to the Lions.
This is one doctor’s outside interpretation, not a diagnosis from Joseph’s medical team and not an announcement from the organization.
Joseph, 25, opened Detroit Lions training camp on the Physically Unable to Perform list after a knee injury limited him to six games during the 2025 season. Players placed on the active/PUP list can be activated during camp, so the designation itself does not rule Joseph out for the start of the regular season.
Still, nobody around Allen Park is pretending this is a routine training camp absence.
Doctor Recommends Retirement for Kerby Joseph
Liao offered an ominous assessment while discussing the possible consequences of Joseph’s lingering knee trouble with Lions On SI.
The doctor explained that a damaged knee can present problems far beyond discomfort, especially if the issue involves articular cartilage and recurring swelling.
“It’s not just a pain management issue,” Liao said. “Swelling is somewhat something that can happen. He’s already acknowledged the swelling was one of his symptoms. We have swelling. You start having decreased mobility in that joint. That joint just can’t move freely anymore. Also, if this is an articular cartilage issue, what articular cartilage does is it allows the joint to glide the bones to glide across each other, and that is damage.”
Liao continued:
“The bones do not glide as well anymore. You get friction, you get heat, you get pain, you get swelling. And you can have these mechanical symptoms of grinding, locking. Things like that that affect your athletic ability.”
Those possibilities sound frightening, particularly for a safety whose game depends on acceleration, sudden changes of direction and the ability to cover large portions of the field.
The key word, though, is if.
Liao is discussing what could be happening based on public information. He does not have the benefit of examining Joseph, studying his scans or observing the full rehabilitation process. Only Joseph, the Lions and the specialists directly involved in his care know the exact condition of the knee.
Retirement Advice Comes With a Major Disclaimer
Liao said Joseph’s best outcome away from football might involve ending his career before additional damage affects the rest of his life.
“The worst-case scenario, as long as he starts ramping up, pain, swelling, disability one or two days afterwards, just like we saw last December. And strangely, this might actually be the best case scenario for the rest of his life. Meaning the best-case scenario for his life may be to early retire and not continue to put this impact damage on his knee, allowing him for as comfortable of a life for the rest of his life.”
He later made the recommendation more personal.
“He’s still so young. It’s unfortunate, but these things come for all of us eventually. This type of cartilage wear and tear, arthritic type issues comes earlier than others. Unfortunately for Kerby, it appears that it might have come for him in his mid-twenties. He’s got a long, long life ahead of him. So, if this is my son or if this is myself, maybe I’m advising that maybe you don’t want to continue to put damage on your knee, because you don’t want to have chronic pain the rest of your life. You don’t want disability in your life. You don’t want future surgeries in your life.”
That is a powerful statement. It is also an opinion formed from a distance.
There has been no public indication that Joseph’s treating physicians have recommended retirement. The Lions have not announced that his career is over, and Joseph has continued working toward a return.
Detroit’s decision to proceed slowly should not automatically be interpreted as a countdown toward retirement. It may simply reflect the reality that the team cannot learn much until Joseph’s knee is exposed to football movements and repeated impact.
Lions Still Need to See How the Knee Responds
Head coach Dan Campbell has acknowledged uncertainty throughout Joseph’s recovery. Earlier in the offseason, Campbell said the organization was gradually increasing Joseph’s workload while trying to build enough strength and stability in the knee.
That uncertainty is why training camp matters.
Running, lifting and controlled rehabilitation can provide useful information. They cannot fully recreate planting against an NFL receiver, breaking downhill to tackle a running back or absorbing contact while moving at full speed.
Joseph’s knee must eventually answer those questions.
Does it swell after consecutive days of work? Can he change direction without losing explosion? Can he recover quickly enough to practice again? Can he perform at a level that makes playing worthwhile?
Until that testing occurs, every outside prognosis carries a large degree of speculation.
Joseph has recently expressed optimism and leaned heavily on his faith during the recovery process. He has also acknowledged that the injury has been a long and difficult battle.
That does not guarantee a comeback. It does show that Joseph has not publicly surrendered to the idea that his career is finished.
Detroit’s Defense Has Plenty Riding on Joseph
The Lions are not waiting on an ordinary starter.
Joseph emerged as one of the NFL’s premier playmaking safeties before his knee derailed the 2025 season. The 2024 first-team All-Pro has recorded 20 interceptions across his first 55 regular-season games, giving Detroit a true center-field defender capable of changing games with one read.
That skill set is not easily replaced.
A healthy Joseph allows Detroit to disguise coverages, challenge quarterbacks and let Brian Branch move around the formation. Without him, Kelvin Sheppard’s defense loses its best deep-ball hunter and one of its strongest answers against aggressive passing attacks.
The Lions prepared for uncertainty by adding veteran defensive backs, including Christian Izien, while building additional depth behind Joseph and Branch.
Depth can keep a defense functional. It cannot fully replace an All-Pro in his prime.
Detroit must also avoid letting Joseph’s status become the only plan. Hope is understandable. Depending on a player whose knee has not yet proven it can withstand NFL work would be reckless.
Brad Holmes and the Lions’ front office have to prepare for both outcomes at once.
Lions Fans Should Avoid Declaring Joseph Finished
Lions fans have every right to be concerned. Joseph missed most of last season, began camp on PUP and still does not have a firm return date.
Retirement talk takes the conversation into a different territory.
An outside doctor raising the possibility is newsworthy. Treating that possibility as a confirmed medical verdict would be irresponsible.
Liao may eventually be proven correct. Joseph could ramp up his activity and discover that the knee cannot handle the pounding required to play safety in the NFL. He could also respond better than feared, return gradually and carve out a meaningful role in Detroit’s defense.
Right now, neither outcome has been established.
The next meaningful update will not come from a social media post or a remote evaluation. It will come when Joseph begins performing football activities and the Lions see how his knee responds afterward.
Bottom Line
Dr. Jimmy Liao believes Kerby Joseph should consider retirement if continuing to play would expose him to chronic pain, disability or additional knee damage.
That warning deserves attention, but it must remain in the proper context. Liao has never examined Joseph’s knee and does not possess the same medical information as the doctors treating him. His recommendation is one outside opinion, not a diagnosis and not proof that Joseph’s career is over.
Detroit fans can be concerned without writing Joseph’s football obituary.
The Lions still need answers. Joseph still wants to return. Until his knee is tested under a true football workload, the most honest conclusion is also the least dramatic one: nobody outside the organization knows how this will end.
