INDIANAPOLIS — It was the kind of continuity rarely seen these days in the National Football League.

On Oct. 14, 2018, the Indianapolis Colts trotted out Anthony Castonzo at left tackle, Quenton Nelson at left guard, Ryan Kelly at center, Mark Glowinski at right guard and Braden Smith at right tackle for their Week 6 matchup against the New York Jets.

Over the course of the next 21 straight games, including the playoffs, those five big stalwarts up front wouldn't miss a single start together — forming by far the longest such streak in the league.

On Sunday, almost two years to the day since that Jets matchup, the Colts' offensive line will have a new starter, however, as Castonzo has officially been ruled out of Indy's Week 5 matchup against the Cleveland Browns with a rib injury.

In steps fifth-year veteran Le'Raven Clark, who will be making his first start since Week 5 of the 2018 season.

Colts head coach Frank Reich said he's expecting Clark to step in and play well in place of Castonzo on Sunday.

"I'm excited to see Le'Raven play," Reich told reporters today. "He came in here this year — I thought he had his best training camp. He's looked as good as he's looked in the three years I've been here. I really think he's going to come in and play well. He's a very athletic guy, smart guy, tough guy."

The 6-foot-5, 311-pound Clark, the Colts' third-round (82nd-overall) pick in the 2016 NFL Draft out of Texas Tech, has played in 39 games with 12 starts to his credit over the past four-plus seasons. He had a bit of a rocky beginning switching between guard and tackle his first couple seasons, but seemed to have taken major steps forward in 2018, when he was asked to start four games at the beginning of the season in place of an injured Castonzo.

Clark didn't appear in a single game in 2019 due to the Colts' continuity up front with the Castonzo/Nelson/Kelly/Glowinski/Smith lineup, but after hitting free agency for the first time in his career this offseason, the Colts brought Clark back on a reported one-year deal to continue to provide much-needed depth up front.

Reich said Clark — who has played 10 snaps at left tackle this season, all coming over the last two weeks — has always kept himself ready to go if needed.

"What I appreciate about Le'Raven, even during this stretch where all of our guys have stayed healthy, he stays locked in, he's always getting himself mentally and physically ready," Reich said. "So I have a lot of confidence in Le'Raven."

Clark faces a tough task on Sunday against a Browns (3-1) defense that ranks eighth in the league in sacks (11), and features a perennial Defensive Player of the Year candidate in defensive end Myles Garrett.

Although Garrett has primarily lined up against right tackles this season, Reich is fully expecting the league's co-leader in sacks (five) to test Clark throughout the afternoon on Sunday, too.

"The thing is with Myles Garrett and what they do defensively, they move him around," Reich said. "So I'm sure he'll switch sides — that's nothing new for him. They'll want to test out Le'Raven and that kind of stuff. But we have our plans on how we'll handle those things. We go into every week with a protection plan, no matter who we're playing — and no matter who's playing for us. It's a comprehensive plan; we build into that plan adjustments that we can make in-game. That gets a lot of work, that protection gameplan."

And, if needed, the Colts could always slide some extra protection Clark's way on Sunday, but that also takes another potential contributor in the passing game out of the mix.

"That is the balance each and every week," Reich said. "You pull on one part of the spider web, it affects everything else in the web. So you want to keep a guy in to help in protection? It comes at the cost of not getting a fifth man out in the pattern. And so that's the decision coaching staffs are making every week, especially when you play a team that has somebody like Myles Garrett, or they have a rusher like him, that's the advantage, when a guy requires that much attention, it's pulling from something else.

"And that's always a fine line, and so the way we approach it is we try to stay balanced; we're going to do a little bit of everything," Reich continued. "We'll give a little bit extra help, we'll throw some rhythm passing game, you want to run the ball enough to kind of keep them neutral. That's the best you can do, and we feel confident that as an offense and as a team that we can do that and neutralize them to the degree that we need to to win the game."

As for Castonzo, while his injury is not believed to be too serious, Reich on Friday wasn't yet prepared to attach any sort of definite return timeline to his veteran left tackle.

Reich acknowledged holding Castonzo out on Sunday was a "safe" measure, but because rib injuries can be so unpredictable — and because you want them to fully heal before a player can return — it's tough to say right now when No. 74 could get back into the lineup.

"I mean, we were every day just kind of checking in with him on how he felt, and you guys know how a rib thing is — you just wanna let it get settled down, and the littlest thing can aggravate it. But then once it's healed, it's healed. You know, that's what you're hoping," Reich said. "So as the week went on and as we saw, OK, you know, you hold out a little bit of hope, maybe you practice later in the week and play, but once you determine that that's not gonna happen like today, it was like, 'OK, let's not practice. Let's get through the weekend and then re-evaluate next week and let the thing heal up the best we can, whether it takes one week, or two weeks or whatever it takes to get him back for the long haul.'"