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INDIANAPOLIS – Nick Sirianni is a bit preoccupied these days. He’s got J.J. Watt on his mind and for good reason.

Not only are Sirianni and the Indianapolis Colts’ offense preparing for another meeting with the Watt-fueled Texans Sunday in Houston, they’re doing so without arguably their most irreplaceable component.

That would be left tackle Anthony Castonzo, who’s expected to miss a few games after spraining the medial collateral ligament in his right knee in last Sunday’s loss to the Tennessee Titans.

At one point during a Tuesday Zoom conference call, Sirianni described Castonzo “a dominant left tackle.’’ A few seconds later, it was “unique’’ and “elite.’’

You get the idea. No one should question Castonzo’s value to the Colts. They’re 2-11 when he’s missed a start during his 10-year career, and the offense came to a screeching halt after he sustained the knee injury early in the second quarter against the Titans.

And no one should question the level of threat posed by Watt, or his ability to draw the undivided attention of the upcoming offensive coordinator.

“He’s been not a good player but a phenomenal player in this league for a lot of years,’’ Sirianni said. “I have the utmost respect for J.J. Watt.

“We have thought about J.J. Watt more than you could possibly think about a person these last couple of days, yesterday and today. We will continue to think about him as the week goes along. We don’t want to let a good player beat us.’’

Sirianni quickly corrected himself.

“Not a good player but a great player beat us,’’ he said. “We’ll do everything we can to slow him down. He’s going to be able to get his because of how good of a player he is, but unique players like him, we’re definitely going to focus on and have a plan for cause obviously he is such a phenomenal football player.

“Thinking about him a lot and how we’re going to slow him down.’’

That starts with probable backup Le’Raven Clark once again replacing Castonzo. There are other options, including flipping right tackle Braden Smith to the left side. However, Smith was a guard at Auburn who was moved to right tackle as a rookie when injuries decimated the position. It’s believed he’s never played left tackle.

Moving Smith to left tackle would impact two positions.

“Obviously the chemistry is greatly important,’’ Sirianni said, adding the coaching staff “plays out every scenario. What’s the best fit for our team? What’s the best fit for our team this week? We have a ton of conversations going on about that.’’

Again, it seems most likely the Colts stick with Clark at left tackle and provide him with whatever amount of help is deemed necessary to deal with Watt and Whitney Mercilus, the outside linebacker who shares the team lead with Watt with 4 sacks.

With Castonzo at left tackle, the Colts seldom feel the need to give him help with a tight end on his side. Sirianni was asked if he could count on one hand the number of times each game the team gave Castonzo help.

“Yeah, probably,’’ he said. “He’s a unique player in that aspect.

“Any good defensive end we have to account for whether Anthony’s there or whether Anthony’s not there. What Anthony does give you is he is a dominant left tackle that is able to win his one-on-one matchup. We just have to be aware that there might need to be a little help for whoever’s in there because Anthony’s elite, so we might not look exactly the same.’’

Watt is in the 10th year of a Hall of Fame career. He was the 11th overall pick in the 2011 draft, the same draft that delivered Castonzo to the Colts with the 22nd overall selection.

He’s a three-time Defensive Player of the Year and his 100 sacks rank 4th among active players. Watt also has been credited with 165 tackles for a loss and 274 QB hits.

No one needs to get the Colts up to speed with Watt’s ability to impact a game. He’s had 12 sacks, 34 QB hits, 20 tackles for loss and three forced fumbles in 13 games against Indy, including at least 1 sack in seven games.

The Texans maximize Watt’s game-breaking skills by moving him from the left side to the right, and lining him up inside. He probes for a weakness and exploits it.

In week 4 of the 2018 season, Castonzo was out with a hamstring injury and Smith had yet to be inserted into the starting lineup when the Texans visited Lucas Oil Stadium. Clark was at left tackle and Denzelle Good at right tackle.

The Texans hounded Andrew Luck throughout. They got to him for four sacks – two each from Watt and Jadeveon Clowney – and six other hits in the pocket, and eventually won 37-34 in overtime. Watt forced two fumbles.

The Colts’ pass protection was similarly leaky earlier this season when a rib injury sidelined Castonzo at Cleveland. Rivers was only sacked once and the Browns credited with four other hits, but Rivers endured his worst game of the season.

Last week against the Titans, the pass protection was stout early but degraded when Castonzo exited.

With Castonzo protecting Rivers’ blindside, the offense generated 141 yards and touchdowns on its first two possessions. Without him and with Clark at left tackle, the Colts’ next six drives consisted of five punts, an interception and 58 total yards.

The Titans turned up the heat, and, at least early, much of it came from Clark’s end of the line. They finished with 2 sacks and four other QB hits. Rivers completed just 57.1% of his passes, his second-least efficient game of the season.

How about Quenton?

Quenton Nelson has established himself as one of the NFL’s premier guards. The 6th overall pick in the 2018 draft is a two-time, first-team All-Pro.

How would Nelson fare if the Colts slid him out to left tackle?

“Quenton would probably be good at left tackle,’’ Sirianni said. “He’s such a good football player, he’s probably be good there. Have I seen him play that? Haven’t seen him play, but do I think he could do it? Yeah, because I think Quenton’s just a heckuva football player.

“I think he probably could play center, he probably could play left tackle, probably play right tackle. We handed him the ball last year, and he didn’t get in the end zone as a fullback. He catches it all right, too, so maybe he could play some wideout, maybe in the slot.’’

You can follow Mike Chappell on Twitter at @mchappell51.

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