Happ had declared for the 2018 NBA draft but didn't sign an agent, giving him until Wednesday to pull his name out of the draft.
The 6'8" player averaged 17.9 points and 8.0 rebounds per game last season.
He also averaged 3.7 assists, 1.5 steals and 1.1 blocks per game, leading the Badgers in every category.
Despite his production in college, he wasn't considered much of an NBA prospect in this class. He isn't listed among the top 30 prospects by Bleacher Report's Jonathan Wasserman, a problem for someone hoping to be taken in the first round.
"So far, with the teams I’ve worked out for, (the projection) has been late-second round," Happ said Monday, per Vince Ellis of the Detroit Press Press. "With that, I’d rather go back to school. There’s no guarantees unless you’re early in the first round. There’s so much stuff that happens in the first 30 picks that there’s no way to guarantee a spot, but it’s great to get in as many teams as possible and they help to do that."
On the plus side, he has a chance to make a major impact in 2018-19 for a Badgers team coming off a disappointing season.
Most of the rotation will return alongside Happ, who could be one of the best players in the Big Ten next year. He was already named first-team All-Conference by the media last season and Carsen Edwards will be the only other returning player on the list.
If he can continue to improve, the Wisconsin star has the talent to be an All-American as a senior.