CHAMPAIGN, Ill. (AP) — The dark mood that set in around after Illinois' loss to Purdue on Saturday turned darker Sunday when X-rays revealed quarterback Wes Lunt has a broken left leg.

Illini coach Tim Beckman said in a news release Sunday that Lunt broke his left fibula during the 38-27 loss to the Boilermakers and will be out four to six weeks. Beckman was optimistic the redshirt sophomore could return late in the season.

"I'm very disappointed for Wes, his family and the Fighting Illini family, but I know we all will respond to this situation in a positive way," Beckman said. "He's having an outstanding season and we're very hopeful to have him back on the field for the final three games."

Illinois (3-3, 0-2 Big Ten) will now turn to backup Reilly O'Toole and third-stringer Aaron Bailey, Beckman said. Bailey is a more mobile signal-caller the Illini had talked about red-shirting.

"We have a lot of confidence in Reilly O'Toole and Aaron Bailey as we prepare for our upcoming game against Wisconsin," Beckman said.

Lunt is 18th in the nation in passing yards with 1,569 and 17th in touchdowns with 13. The transfer from Oklahoma State leads in the Big Ten in passing yards per game with 313.8.

Lunt limped off the field after a big hit in the fourth quarter of the Purdue game and didn't return.

After the game he described the injury as "like a contusion" in his calf and said he thought that was an injury he initially suffered several weeks ago against Washington.

"It's really tight, hard to put pressure on it so we'll get an X-ray and see what's going on with it," Lunt said at the time.

O'Toole has played in two games, going 30 of 57 for 428 yards, one touchdown and four interceptions.

The passing game without Lunt isn't nearly as dangerous as it is with him, and Illinois' run game is limited. The Illini ran for 65 yards on 25 carries against the Boilermakers.

The Illini came into Saturday's game expecting a win over the Boilermakers that would keep them moving toward bowl eligibility. In just over 24 hours the team's course changed dramatically.

Given the date Saturday with a Wisconsin team coming off an upset loss to Northwestern, Illinois will be challenged to avoid letting the Purdue loss and Lunt's injury become the dominos that sets others tumbling.

"It's over, it's done with," offensive coordinator Bill Cubit first insisted after the Purdue game, then admitted he wasn't quite ready to let go. "I'm sure I'll be thinking about it. I'll lie in bed and not get much sleep."

Illinois' defense remains a major problem, too.

Purdue had 551 total yards, 349 of them on the ground. That's from a team that came into the game averaging 312 total yards game.

"You work so hard," a subdued Tim Banks, the Illinois defensive coordinator, said. "We knew coming into the game that those guys wanted to run the football."

It won't get easier with Wisconsin (3-2, 0-1). Even in the Northwestern loss, Melvin Gordon ran for 259 yards.

A chorus of Illini fans called on Twitter in the hours after the game for Beckman to be fired, with some throwing Banks' name in, too.

Beckman has coached under pressure since his team won two games in his first season in Champaign.

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Follow David Mercer on Twitter: https://twitter.com/davidmercerap