Appling, a senior Izzo called his team's top defender, first hurt his wrist Dec. 4 against North Carolina but played in every game until Thursday's win against Penn State.
The Spartans got Adreian Payne back Thursday from a foot injury that caused him to miss seven games, but Izzo said a timeframe for Appling's return is unclear.
"I have no idea," Izzo said, according to MLive.com. "This has been the most frustrating. It's beyond disgusting. I have no timeframe. I know he won't practice tomorrow. Whether he does on Saturday or plays Sunday or whether we're going (to Wisconsin) without him, I wish I could tell you. If I knew, I'd tell you."
Izzo said that Appling's wrist had improved since the North Carolina game but that he has aggravated it in Big Ten play.
"I can't tell you what it was like yesterday," Izzo said. "I'm sitting in my office preparing for practice. I talked to Keith the night before and it sounded like things were getting better. Then the trainer calls and says, 'He can hardly move his wrist.'"
Although Payne returned to score 12 points in 18 minutes, Michigan State is still without Branden Dawson, who has a broken hand.
Despite all of its injury woes, No. 9 Michigan State is tied for first with rival Michigan atop the Big Ten. Everyone else in the conference is at least three games back.