GREEN BAY, Wis. -- Brett Favre opened his Pro Football Hall of Fame induction speech with a joke. Well, we think it was a joke.

“I’m going to ask Mike McCarthy and Ted Thompson if I can play the first series tomorrow night,” the legendary Green Bay Packers quarterback said, referring to the team’s head coach and general manager seated in the crowd.

ESPN’s cameras then cut to Aaron Rodgers, Favre’s successor and the team’s current starting quarterback. Rodgers just smiled and shrugged, knowing that he won’t be under center for the first snap of Sunday night’s Hall of Fame Game between the Packers and Indianapolis Colts, either.

But as good a story as it might be to see No. 4 one more time in green and gold, the alternative narrative isn’t too bad, either.

With Rodgers slated for a DNP-Coach’s Decision and No. 2 quarterback Brett Hundley out with an ankle injury he suffered during practice on Monday, the Packers will start undrafted rookie free agent Joe Callahan, who just happened to be born in 1993 -- following Favre’s first season in Green Bay -- and grew up loving the Ol’ Gunslinger.

“It’s pretty cool how that all worked out. He was my favorite player growing up,” Callahan said before the team left Green Bay on Saturday. “I tried to play like him when I was a kid. Then getting signed by the Packers and now this whole Hall of Fame Game the year of his induction, it’s a pretty cool experience and great to be a part of.”

Rodgers said in an interview on ESPN Wisconsin’s “Wilde & Tausch” that some of the guys in the locker room have taken to calling Callahan “Bo,” after the fictional University of Wisconsin quarterback who is the presumptive No. 1 overall pick in the 2014 movie “Draft Day.” But while that Callahan’s challenge entering the NFL was not being taken with the top pick, the real-life Callahan is facing a much greater challenge.

After all, a year ago, he was getting ready for a big season-opening showdown with … Frostburg State.

“I’m preparing for a little bit different of a game this week than I was last year,” Callahan said with a smile.

Coming from tiny Wesley College in Dover, Delaware, the 6-foot-1, 216-pound Callahan knows the deck is stacked against him -- despite a record-setting career that saw him throw for 5,063 yards and 55 touchdowns last season and win the Gagliardi Trophy, Division III's version of the Heisman.

But he’s done everything he can to improve his chances, including being tutored by ex-NFL quarterback Jay Fiedler and draining the battery on his iPad playbook, digesting as much of the Packers’ complex scheme as he can.

“I’m just making sure that I’m preparing every night, making sure I’m in the book studying and trying to be as ready as possible for Sunday,” Callahan said. “I feel good. I feel good with the game plan that we’ve put in and my level of preparation for it.”

Although associate head coach/offense Tom Clements acknowledged the obvious – “There’s still a long way to go,” he said – quarterbacks coach Alex Van Pelt did say that he’s “definitely seen big improvements in Joe since the first day he’s gotten here.”

That probably isn't enough to earn Callahan a spot on the 53-man roster -- with a few ultra-deep positions elsewhere -- it’s likely that the Packers will break camp with just Rodgers and Hundley on the 53. But if he performs well enough Sunday night and throughout the preseason to convince the Packers of his potential, he could land on the practice squad as their developmental third quarterback.

For now, he’s competing for that opportunity with Marquise Williams, a three-year starter at North Carolina who has the edge in big-game experience but didn’t join the Packers until a month after Callahan, having first attended the Minnesota Vikings’ post-draft rookie camp.

“It’s going to be awesome,” said Williams, who worked out for the Packers in late May, then flew home only to learn of the Packers’ decision to sign him as he touched down at the airport in Charlotte. “As a child, you’re growing up [picturing] yourself playing in the NFL. [Your] third-grade teacher asks you what do you want to be when you get older and I always wanted to be an NFL quarterback. It’s going to be a great time.”

It may also be a nerve-wracking time. One of the scenes included in Favre’s presentation video showed former Packers head coach Mike Holmgren telling his star quarterback to calm down over the headset. Callahan would be wise to keep Holmgren’s advice to Favre in mind.

“First NFL snap, there’s definitely going to be some nerves, but then there’s going to be a lot of excitement, too,” Callahan said. “I’m going to try and make sure I’m level-headed and calm so I’m not firing the ball all over the place. That’s one of the things: Don’t let my emotions get the best of me.”