Here's what kind of injury the Houston Texans' star has.
J.J. Watt suffered a tibial plateau fracture in the first quarter of the Texans' loss to the Chiefs on Sunday night.
Houston's star defensive end had to be carted off the field and taken away in an ambulance.
Watt is out indefinitely and will undergo further testing, though surgery is expected and he's likely to miss the rest of the season.
It's believed that the injury Watt suffered is a "more severe trauma" than a torn ACL.
This is the play that caused it:
Watt, a three-time NFL Defensive Player of the Year, missed the final 13 games of the 2016 regular season with a back injury.
He says he is "devastated."
A sixth-month recovery period is expected.