"This game can be beautiful and it can also be brutal," Watt tweeted Sunday. "Absolutely gutted that I won't be able to finish the season with my guys and give the fans what they deserve. I truly love this game and can't stand letting you guys down. Thank you for all of the thoughts & well-wishes."
The Texans fear that Watt tore his pectoral muscle, sources confirmed to ESPN's Dianna Russini. Watt also referenced his pec in another tweet after Sunday's game.
"It's tough," quarterback Deshaun Watson said of losing Watt. "That's a big part of this team. But he knows that this locker room, this organization, this town, this city, the Houston nation is definitely going to support him through his recovery. We always love him. He's going to be right there with us. Important, helping us out.
"You hate to just see, not just him, but anybody go down and any injury, especially a season-ending injury. All the work that he put in to get to this point. It's crazy and it sucks, but we all send our prayers towards him. We love him, and we're definitely going to support him."
Watt appeared to injure his pectoral muscle while tackling Raiders running back Josh Jacobs for a 6-yard loss in the second quarter. Watt left the field for the Texans' blue medical tent before running to the locker room. The Texans first announced he was questionable to return to the game before later ruling him out at the start of the third quarter.
"We feel terrible for him. He works so damn hard, and he's such a good person. Can't replace him on or off the field," a source told Russini.
Before he left the game, Watt had three tackles, a tackle for a loss and a pass defended. Watt has four sacks this season, but ESPN's pass rush win rate powered by NFL Next Gen Stats shows the impact Watt has had on the field. Watt created the first pressure on 62 pass rushes, easily the most in the NFL. No other player had more than 49 first pressures created.
Watt also created 19 incompletions via first pressure, which is the most of any player in the NFL. Watt was able to have that success despite being double-teamed on 29.8% of his pass rushes as an edge rusher. Only Jadeveon Clowney was double-teamed at a higher rate as an edge rusher this season.
Watt, 30, did not miss a game during the first five seasons of his career, but he has finished the year on injured reserve in three of his past four seasons. In 2016, Watt only played in three games before undergoing season-ending back surgery. The following year, Watt broke his leg in Week 5.
Last season, Watt played in all 16 regular-season games, finishing the season with 16 sacks, which ranked second in the NFL.
Texans outside linebacker Whitney Mercilus is the only other proven pass-rusher that Houston has right now, after trading Clowney to the Seahawks before the start of the season. Mercilus has had a strong first half, with 5.5 sacks, four forced fumbles, a fumble recovery and an interception.
"We've had moments like these," Mercilus said. "It's nothing new to us. When we have situations where it might seem like we're down and people are counting us out, all we do is put our heads down and keep trucking down and make plays.
"As you've seen out on the field, you've seen guys stepping up and making plays. ... It's the next-man-up mentality. We've had injuries in the back end. Those guys have done a great job stepping up making plays for us. It just means we've got to double down on some efforts."
Texans coach Bill O'Brien said the chances are "slim to none" of the team trading for a defensive end to mitigate the loss of Watt.
"No one person is going to take the spot of a Hall of Fame player," O'Brien said Monday. "But at the end of the day, these things happen, and we've got to move forward and do what we have to do to win games."
Watt injures shoulder on tackle
J.J. Watt leaves the field and goes back to the locker room with a pectoral injury after making a tackle in the second quarter.