MADISON, Wis. -- Wisconsin coach Bret Bielema wants to be clear about how he feels about his defense that gave up 564 yards against Michigan State on Saturday.

He said he's not frustrated, he's just displeased. But Bielema said it is frustrating to see players making the same mistakes over and over.

The defense gave up three single plays for more than 50 yards each. But the No. 5 Badgers still won and remain undefeated.

However, they are the underdog against unranked Illinois this weekend.

Bielema said his defense knows they have to play better. It has been inconsistent this year despite returning key starters and being among the best in the nation last season.

Wisconsin is riding a nation-leading 14-game winning streak.

Illini Favored To Beat Badgers But Zook Has Doubts

Gamblers think Illinois will knock off Wisconsin in Champaign on Saturday, but Illini coach Ron Zook thinks those odds are a little off.

Illinois is favored by 3.5 points to beat the Badgers.

Zook joked Wednesday morning that a Wisconsin fan must have made his team the favorite, hoping to rile the Badgers. Zook said there's no reason that a team like Illinois, which had just two wins in each of the last two seasons, should be favored over a power like Wisconsin.

This year, however, the Illini are 4-1 and fresh off a 27-20 upset of Penn State. The Nittany Lions were ranked 21st in the country before the loss.

And Wisconsin's 5-0 record includes close wins over unranked teams Nevada-Las Vegas, the Citadel and Iowa.