HOUSTON - JJ Watt is the heart and soul of the Houston Texans. Sunday night he went down and an entire city held its breath.

The defensive end exited the Houston Texans' game against the Kansas City Chiefs on Sunday night after a left leg injury in the first quarter. He was helped off by trainers and later was carted to the team's locker room.

"I could see during that play that his knee gave out," said Dr. Patrick McCulloch. McCulloch is an orthopedic surgeon at Houston Methodist Hospital and the team physician for the Houston Astros. He's treated athletes facing the same injury #99 is facing now.

"It's an injury that happens in a critical place," said McCulloch. It's called a tibial plateau fracture. And McCulloch says it's a much more serious type of leg fracture.

J.J. Watt: 'I can't sugarcoat it, I am devastated.'

"When you have a fracture on the tibial plateau it means it comes up right to the knee joint and that has implications because it means it's not just the bone that's broken but the cartilage overlying the bone has also been damaged," said McCulloch. It's extremely painful, too.

"You get blood and swelling in the knee too, so it makes it particularly uncomfortable," said McCulloch.

Watt was in tears as he was helped off the field Sunday night, another season over due to unexpected injury. McCulloch says repairing that type of injury can pose complications.

"Even if we can line the bone back up perfectly remember, bone heals great to bone, but cartilage doesn't always heal to cartilage, and if it's off just a little bit, over time that subtle tear can lead to arthritis," said McCulloch.

Recovery time will depend on the severity of Watt's fracture. It will likely be a minimum of six months until Watt's ready to compete at a high level.

CBS Sports reports Watt will undergo knee surgery Monday. Fans hoping this latest injury doesn't prevent Watt from ever returning to the peak performance Houston is used to.

"This is the adversity they face on a regular basis, and how they deal with it is a measure of a champion," said McCulloch.