ANDERSON, Ind. — A rookie could be making his professional debut for the Indianapolis Colts on Sunday as a starting offensive lineman.

It's just not who you might've expected a week ago.

Joe Haeg, whom the Colts selected in the fifth round (155th overall) in April's NFL Draft, could get the nod at right tackle after starter Joe Reitz suffered a thigh injury during Thursday's training camp practice at Anderson University.

Haeg, a North Dakota State product, was seen getting a majority of the reps at right tackle after Reitz's departure on Thursday and Friday.

The Colts take on the Green Bay Packers Sunday night in both teams' preseason opener in Canton, Ohio.

"The main thing is it's just got to be a learning experience," Haeg said Friday after the team's eighth training camp practice of the year. "You know, being able to go against whoever's out there, I'm just embracing it for however long it is and just trying to make myself better, become a better teammate, and more available for this team just however I can."

A former walk-on at North Dakota State — where he won an NCAA Division I FCS National Championship all five years he was a member of the program — Haeg developed into a First-Team All-American in 2014 and 2015 at both the right and left tackle spots, primarily protecting quarterback Carson Wentz, the No. 2-overall pick in this year's draft.

But with the Colts, who hired Joe Philbin to coach the offensive line in January, the emphasis this offseason for the big men up front has been versatility. As such, Haeg — especially recently — has spent much of his time developing at the guard position, where various techniques are a little bit different than they are on the outside.

But each time Haeg learned a new play or scheme, he said he made sure to always keep a mindset that he needed to know how to execute at any position up front, something that was a big boost when his number was called during Thursday's practice.

"You're not thinking, 'OK, I know for sure I'm right guard. I need to only worry about what the right guard's doing.' You have to learn what every position's doing," Haeg said. "At first, it takes a lot to process. But once you get it, you know what everyone's doing and they can help you out in so many ways, so it's kind of like a blessing in disguise."

Colts head coach Chuck Pagano praised Haeg's work thus far, and said the rookie will likely get work at both tackle and guard during Sunday's game.

"He's a smart guy — tough guy," Pagano said Friday. "(He's) getting mostly guard snaps but he's been doing some tackle work, not only in some team stuff but the pass rush stuff. He's a good player. He loves ball so we're going to get him some work at both in this game and just see what he can do."

Haeg said he's going to try to be "focused, but also loose" on Sunday for his first-ever professional football game. While he certainly has a job to do, Haeg wants to be sure to take in all the moments — big and small — that only come once in an NFL player's career.

"You're out there to play — you want to show the coaches what type of player you are and kind of go out there and prove yourself," he said. "But at the same time, I'll just kind of feed off the energy.

"Yeah, it'll be my first NFL game. It's something I'm very excited for, and I'm just hoping to feed off it and play as well as I can."