Doctors and trainers who have reviewed the video of last Sunday's Texans-Seahawks game think that Houston quarterback Deshaun Watson initially injured his right knee in the fourth quarter and could have even torn his ACL in that game.

The Texans still think Watson tore the ACL on Thursday, but they are aware of and curious about the hit their quarterback absorbed Sunday, per team sources.

With the Seahawks leading Houston 27-24, Seahawks defensive end Frank Clark jumped over Texans running back Lamar Miller and rolled up on Watson, who immediately grabbed his right knee on the play. Watson finished the game, didn't complain about the injury after it and did not get treatment on it last week, per sources.

Watson then fell to the ground in practice on Thursday, when Texans trainers determined their quarterback suffered a season-ending torn ACL. Watson has not decided when to have surgery, but it is considered an eight- to nine-month recovery, per a source. Watson made it back from this injury in college in five months, however.

Doctors and physical trainers who reviewed Clark's hit on Watson said the quarterback planted and then went to an internal rotation of his femur with stress on his knee -- the makings of an ACL injury.

"I can't be 100 percent sure," one doctor said of the chances that Watson tore his ACL against Seattle, "but I wouldn't be surprised. Something happened as he grabbed his knee. And if you look at it in slow motion, one mechanism of injury is there."

Doctors and trainers said they have seen athletes play full games on torn ACLs only to complain about knee pain later. So while many believe Watson tore his ACL on a run-option play during Thursday's practice, it's possible he initially injured his ACL and possibly even tore it last Sunday in what turned out to be the final game of Watson's rookie season.

What makes it all the more impressive is Watson thrived down the stretch. After the collision with Clark, Watson completed 4 of 5 passes for 144 yards and two touchdowns. He also ran the ball once for 8 yards.

Doctors also said it's possible that the hit Watson took last Sunday affected the knee to the point that it made it ripe for the ACL to later be torn. One doctor pointed to the case of Dolphins quarterback Ryan Tannehill playing on a compromised knee before it gave out during a training camp practice last summer.

During his freshman season at Clemson in 2014, Watson played with a torn ACL in his left knee, coach Dabo Swinney said at the time. He later had surgery and missed the Tigers' bowl game against Oklahoma.