Mark Dantonio thought he had endured just about everything in his first 99 games as Michigan State's coach.

He recovered from a heart attack in 2010; lost the inaugural Big Ten championship game to Wisconsin in 2011; dealt with a string of narrow losses in 2012; and celebrated all those blowout wins in 2013 that ended with the Spartans' first Rose Bowl victory in 26 years.

Game 100 has become every bit as challenging.

Dantonio opened the week by announcing No. 8 Michigan State had signed a prep player, scouted high school tapes of Indiana's projected new starting quarterbacks, and ended the week wondering if all that extra work might be nullified.

"It's a little bit different. Chris Covington was the guy who went in for (Nate) Sudfeld last week," Dantonio said Thursday night on his weekly radio show, referring to the Hoosiers' quarterback carousel. "So he has a little bit of history there. But then you start to hear the other guy may be the guy.'"

It's put Dantonio and the defending Big Ten champs completely in the dark for Saturday's showdown at Indiana (3-3, 0-2 Big Ten) — perhaps intentionally.

On Monday, Hoosiers coach Kevin Wilson announced the inexperienced Covington, a true freshman, would make his first college start after Sudfeld sustained a season-ending separated left shoulder last week at Iowa. By Wednesday, it appeared another untested true freshman, Zander Diamont, might make his first college start.

Wilson has not commented on the possible change, which forced Dantonio and the Spartans (5-1, 2-0) to spend even more hours in the film room.

"I guess it's always the unknown that bothers you a little bit," Dantonio said Thursday. "The thing that we have to know is that coach Wilson is going to have a plan, it's going to be a well-designed plan."

Regardless of which freshman starts, Dantonio has some idea of what to expect Saturday: a steady dose of Tevin Coleman, the nation's top rusher; a challenge from Indiana's change-of-pace back, D'Angelo Roberts; and a pair of potential game-changing receivers in Shane Wynn and Nick Stoner.

The uncertainty poses a major challenge for a defense considered one of the best in the nation despite struggling to close out victories each of the past two weeks.

But Dantonio, about to become the fourth Spartans coach with 100 career games, promises to have the Spartans ready for anything.

"They (the Hoosiers) are going to ask that guy — whoever that is because it seems like whoever that is it's going to be a freshman — they're going to ask him to do things they can do," Dantonio said. "There's a reason they're on scholarship, they're good players."

Here are some other things to watch Saturday:

SPARTANS' RUN DEFENSE: Michigan State's run defense might not have looked that good last week when Purdue rushed for 129 yards and three touchdowns. It must be better this weekend against Coleman, who probably will take on an increased workload with Sudfeld out.

TAKING A PASS: While the Hoosiers' defense has improved, Indiana still ranks last in the league against the pass. That could give the Spartans' combination of second-year starting quarterback Connor Cook and playmaking receiver Tony Lippett a chance for another big day.

THE STREAKS: Michigan State has been in a class by itself over the last two seasons. The Spartans have won 12 straight against conference foes, including last year's championship game. They also have won seven straight conference road games and are 5-0 against Indiana under Dantonio. He can tie Charlie Bachman for second in school history with his 70th career win this weekend.

THE LINE: Indiana has a big, experienced offensive line. Michigan State has one of the best pass rushes in the nation. The winner of this battle will likely walk away with the Old Brass Spittoon.

TWO FOR THE SHOW?: When Indiana upset then No. 18 Missouri on Sept. 20, the Hoosiers became the first Big Ten team to beat a ranked SEC team on the road since at least 1980, according to STATS. The Hoosiers now have a chance to upset a second ranked team in the same season, something they haven't done since taking down Oregon and Minnesota in 2004.