MADISON, Wis. — When Oregon State offered Nnanna Egwu a scholarship during his sophomore year of high school at Chicago’s St. Ignatius, the teen was blown away.

“I couldn’t believe it,” Illinois’ 6-foot-11 center said. “I was like, ‘What’s going on?’ ”

Egwu didn’t have visions of playing the game on a big stage growing up.

He was a fan of the game. Watched it on television. Loved the Chicago Bulls.

But Egwu didn’t start playing hoops until he was in eighth grade at a neighborhood park.

“I just did it for fun; it wasn’t really organized,” he said. “My grade school didn’t have a team, so I didn’t play.”

Egwu didn’t intend to play at the academically challenging St. Ignatius, where he and twin sister Nnenna were on academic scholarship. But coaches Rich Kehoe and Ken Gryzwa spotted the gangly 6-5 freshman in the halls and talked him into giving the sport a shot.

Smart move.

He went from project to prospect after a wildly successful prep career with the Wolfpack and Mike Mullins’ Illinois Wolves program.

He’s showing the same rapid progression as a sophomore with the Illini.

Egwu enters today’s game at Wisconsin (1:15 p.m., BTN) as one of the Big Ten’s most improved players.

“His ceiling is so high,” said Illinois assistant coach Dustin Ford, who works with the big men. “It’s high because he’s skilled, but he’s such a good kid, a smart kid, and he works so hard.”

Egwu’s physical gifts — the size, strength and athleticism — are obvious. But his work ethic is what’s impressed his coaches and teammates the most. He goes hard in every drill, every play.

“After the first time I worked with him and I talked to Coach (John Groce) I said, ‘He’s going to be fun to work with for three years,’ ” Ford said. “He listens and his motor and the way he works out is ridiculous. You can’t wear him out. That’s a great quality to have.”

The fruits of Egwu’s labor are beginning to show at a high rate. Twice in the last three weeks he’s set a career high for points: 12 against Missouri and 16 against Ohio State. Buckeyes coach Thad Matta gushed about Egwu afterward.

He grabbed a career-high nine rebounds twice in the last five games and blocked a career-best five shots at Purdue.

“He’s probably played 500 less games in his life than every kid on the Illinois roster. The instinctual stuff has come very gradually, and that’s starting to come together,” Mullins said. “Every time he plays he learns something different. A lot of kids this age don’t have that gift anymore. Either they’re not open to learning or they’ve reached their peak. I don’t think he’s anywhere near his peak.”

The addition of fifth-year senior Sam McLaurin to the Illinois roster has been key to Egwu’s development. The Coastal Carolina transfer matches up with Egwu in practice and relays tricks he’s learned during his playing career.

“He teaches me a lot. He’s been playing for a long time,” Egwu said. “He tells me what to do and ways to do it. He gives great advice. I’ve been glad to have Sam around to help me develop as a player.”

Egwu’s midrange jumper is the strength of his offensive game. He’s shown flashes of developing a low-post scoring attack and has the range to step behind the three-point line occasionally.

“I honestly think that by the time he’s done here, he’ll be a guy that can pick and pop and make threes. I think he can do it now, but that’s not something he’s comfortable with right now, so we’re not going to force him to do that,” Ford said. “I think he’ll be a good low-post scorer before he leaves here, but he’s not comfortable with that yet, so again, we’re not going to force that. It will come.”

A successful student in the classroom, Egwu’s likely to have a lucrative career off the court after graduation if he so chooses.

“He’s going to be successful at whatever he does, I don’t care what it is,” Ford said.

As an eighth-grader at Clarendon Park on Chicago’s North Side, Egwu didn’t dream of an NBA career.

“Since I got here, I’ve said I thought he was a pro,” McLaurin said. “He’s turning a lot of heads now with the things he’s been doing. I definitely think Nnanna’s a pro.”

All the acclaim and attention is news to no one except Egwu himself.

“I don’t pay too much attention to it; I haven’t noticed,” he said. “As long as we continue to win and I can do my part and that keeps going, it can work out for the best.”