HOUSTON (AP) — As the Houston Texans face another long stretch without superstar J.J. Watt, they know the rest of their defense will have to step up to make up for his absence after he and linebacker Whitney Mercilus both suffered season-ending injuries on Sunday night.

"These guys that are there, they're going to have to step in and ... it's going to be multiple guys," coach Bill O'Brien said.

"You don't replace J.J. Watt or Whitney Mercilus with one guy. That's just ridiculous. It's going to be a lot of different guys that are going to chip in to help and I think the coaching staff needs to do a great job, too."

O'Brien confirmed that both were season-ending injuries on Monday, a day after Watt broke his left leg and Mercilus, an outside linebacker, tore a pectoral muscle in a 42-34 loss to the Kansas City Chiefs.

Watt sustained a tibial plateau fracture to end his season early for the second straight year. The three-time Defensive Player of the Year returned in 2017 after missing the last 13 games of last season following his second back surgery.

The defensive end played every game in his first five seasons in the NFL before his injury last year.

Mercilus, who is in his sixth season, started each game this season and had 10 tackles and a sack.

"I feel bad. I can't express it any other way," O'Brien said. "I've gotten to know ... these guys, over the last four years. They mean a lot to me personally. I've asked them to do a lot of different things. I've asked them to be leaders, I've asked them to put a lot of time into this thing."

Jadeveon Clowney, who was the top overall pick in the 2014 draft, has grown into a leadership role on this team and knows he'll have to help the unit figure out a way to deal with the losses as the Texans prepare to host the Browns on Sunday.

"It hurts, a big blow to the team," Clowney said. "A lot of our game plan was around them two. So we've got to find a way to regroup because we've got a lot of season left."

Clowney had a breakout season last year with a career-best 16 tackles for losses after struggling with injuries in his first two NFL seasons to allow the Texans to remain one of the top defenses in the NFL despite losing Watt early. He's kept up his strong play early this season and has 16 tackles, three sacks and has returned a fumble for a touchdown.

"There's no doubt that (Clowney) will be a guy that we count on to play real well for us," O'Brien said.

"He plays very hard, he's been practicing well and obviously he's a guy that, whether J.J. and Whitney were there or not, he's a guy that we really rely on to play at a high level and that's not going to change."

He has lined up at both outside linebacker and defensive end this season, but could see more work at defensive end with Watt's season over.

The loss of Mercilus is the latest setback to Houston's linebackers after veteran middle linebacker Brian Cushing was suspended for 10 games on Sept. 13 for violating the league's policy on performance-enhancing substances.

With Mercilus out, the Texans will look to Brennan Scarlett to fill in. Scarlett signed with the Texans last year after going undrafted out of Stanford. He appeared in seven games last season and has played in each game this year, but has never started.

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