Taylor underwent a magnetic resonance imaging exam Monday that revealed the extent of the damage. He was officially placed on injured reserve Tuesday.

The Texans will promote Jeff Driskel from the practice squad to back up Mills. Pro Bowl quarterback Deshaun Watson (standing trade request, legal problems) will continue to be inactive and will not be practicing.

Taylor completed 10 of 11 passes for 125 yards and one touchdown for a 144.3 passer rating before getting hurt against the Browns during a touchdown run.

Now, the Texans have to adapt to Mills’ style as more of a pocket passer than Taylor, a dual-threat quarterback.

“I think any time you have a different quarterback in the game, you're doing what you can to try to play to his strengths,” offensive coordinator Tim Kelly said. “Davis has done a good job since he's got here coming in and putting himself in a position to go out and hopefully make that transition seamlessly. We're going to still do what we can to make sure we're putting him in a spot to be successful.

“He's got a really good grasp of the offense. I think he can make all the throws. You saw him make some pretty good throws on Sunday. The one to Jordan Akins on third down was really good, as far as his anticipation and his accuracy with that ball. He put it right where it needed to be with the coverage. As far as him being able to operate from the pocket, I think he does that really well.”

The injury changed the complexion of the game as the Texans lost after building a 14-7 halftime lead with Taylor. It also dramatically changes the Texans’ quarterback situation.

Taylor passed for 416 yards, three touchdowns and zero interceptions in two games, completing 70.1 percent of his throws for an 84.6 quarterback rating.

“You feel for your guys," Texans wide receiver Brandin Cooks saidMonday morning. "Everything that he puts into this game and to see him go down like that, it’s crushing. But knowing him, he’s built for it, he’ll find his way back and I bet you he’s grinding right now to come back as quick as he can.”

The Texans don’t plan to dramatically change the game plan with the shift to Mills.

“Basically, just do what we ask him to do,” Culley said. “We'll actually have the same playbook, obviously there's some things that he is a little different than Tyrod, but we actually have the same kind of plays. But we'll use the things that fit him more so than what we did with Tyrod. Some of the things we did with Tyrod we may not do with him in the run game, but as far as the pass game it will basically be the same thing.”

A year ago with the Los Angeles Chargers, Taylor lost his starting job to Justin Herbert when a team doctor accidentally punctured his lung while giving him a pain-killing injection. In 2018 with the Browns, Taylor suffered a concussion and was replaced by Baker Mayfield.

“Losing No. 5 (Taylor) definitely hurts,” center Justin Britt said. “I do not think this is something that, with his career and history I do not think this is one of those scenarios. We trust him.”

Taylor was running away from Browns defensive end Myles Garrett when he got hurt.

Culley said the emergency quarterback isn't something he's sure about. If they had lost Mills to an injury against the Browns, Culley indicated he likely would have used running back Mark Ingram and run the Wildcat formation.

A strong-armed third-round draft pick from Stanford, Mills had his moments during the second half of a loss to a playoff team from last season.

Mills threw a touchdown pass to Cooks. He also had a 35-yard completion to wide receiver Andre Roberts.

"I think you see how it is to be a rookie quarterback that has to get thrown into the fire right away in a hostile environment," running back Phillip Lindsay said. "But as he got more comfortable as things went on, he looked sharp, he looked good, and that’s what it is. Being in Denver, we had different quarterbacks all the time, and young ones, and that’s just how it goes.

"You’ve got to get your feet wet and you’ve got to get used to it, and Davis wasn’t the one taking all the reps at the beginning of the week. So, I’m excited to see what he does as time goes on. He’ll get better as time goes on, so that’s how it goes when you have a young quarterback.”

A former blue-chip recruit from Atlanta who chose Stanford over Alabama and Michigan, Mills was was an honorable-mention All-Pac-12 selection who passed for 1,508 yards, seven touchdowns and three interceptions in five games last season. He set a single-game school record with a 504-yard performance against Washington State. As a sophomore, he passed for 1,960 yards, 11 touchdowns and five interceptions.

Although Mills only started 11 games at Stanford due to a knee injury, he showed enough to impress the Texans and be drafted 67th overall.

“As the backup quarterback or the guy that is next up, you always have to be ready for anything to happen,” Mills said. “I felt like I did a good job. I can improve on some stuff. A lot to learn from, but overall I didn’t think I was too rattled or wasn’t ready for the moment.

“It is kind of just finding that rhythm. Obviously, I would have liked to start a little faster, but that comes with some experience. I’m looking forward to what’s next. I thought the whole team rallied. They had a ton of confidence in me. It allowed myself to go out there, have confidence and do my thing.”

Mills displayed poise and toughness while absorbing some hits, including a sack and forced fumble on a hit by safety Grant Delpit that was recovered by offensive tackle Marcus Cannon.

“Just going out there and playing and not letting the moment get too much for me,” Mills said. “I felt like I handled that well and I felt extremely proud of the guys around me. Obviously, I have a lot to learn from this game, my first true regular season game, so looking forward to the next one.”

It was a jolting hit by Delpit, a former Lamar High School standout who transferred to IMG Academy before signing with LSU.

When Mills entered the huddle as Taylor’s replacement, he got a message from Britt.

“I told him we’re going to be all right,” Britt said. “We did not hesitate. He steps into the huddle and we gave him our full attention and let him control it. They brought him here for a reason."

The Texans have witnessed growth from Mills. How fast he's able to improve as a rookie starter will be pivotal to the Texans' chances.

“The times that he does get in there and practice, he has a command of the offense and the huddle," Cooks said. "A lot more vocal, a lot more confident in that aspect. And just not being quiet, but steps up and talks when he needs to. So when you see that from a young guy and see that build every single day from spring camp until now, that’s been huge.”

The Texans may lean heavily on their running game against the Panthers to take the pressure off of Mills.

“Most definitely, we’re going to try to help him out running the ball, making it a lot less stressful for him as a rookie,” veteran running back David Johnson said. “ I was there, everybody was there. The best thing that you can have is a great veteran group that we have, and then guys who you can lean on to talk to about it.”

Aaron Wilson has covered the NFL for 20 seasons, including the Texans, Baltimore Ravens, Tennessee Titans and Jacksonville Jaguars. He has previously written for The Houston Chronicle and The Baltimore Sun. He’s on Twitter: @AaronWilson_NFL and Instagram: @aaronwilson7128.