LINCOLN, Neb. (AP) Nebraska coach Mike Riley is impressed with the resiliency his team has shown under difficult circumstances the past month.

The Cornhuskers have had to adjust to the absence of popular assistant coach Keith Williams, who was arrested on suspicion of third-offense drunken driving last weekend. His arrest came two weeks after the funeral of punter Sam Foltz, who died in a car crash in Wisconsin along with former Michigan State punter Mike Sadler.

Riley said after practice Wednesday that he has been worried about his players' ability to maintain a focus on football after all that's happened.

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''There have to be things on their mind almost continually,'' he said. ''The thing I'm impressed with is how they perform. They put a smile on their face. For anyone going to work, the attitude you bring and how you present yourself and how you like doing what you're doing means a lot to me about how it's going to go. So for whatever reason, however they've done it with all the stuff that's gone on with these young men, I think they've done really well that way.''

Williams has not been at practice since he was arrested early Sunday after he rear-ended a Uber driver's vehicle in downtown Lincoln. His blood-alcohol level was reported at 0.15, nearly twice the legal limit of 0.08. That high a reading could have led to a felony charge for aggravated DUI. He instead was charged with misdemeanor DUI and cited for careless driving after the non-injury crash. He pleaded not guilty.

Riley had no update on Williams' status with the program.

''This is a most, most, most serious situation,'' he told reporters. ''We are still exploring and talking and finding out as much as we can. This is ongoing right now in-house and because of the seriousness of it, I just don't have anything else to really give you, OK? When I do, it will be definitive and that will be it.''

Graduate assistant Hardie Buck, a receiver and special teams player on Alabama's 2009 and 2011 national championship teams, is coaching the receivers in Williams' place.

''We've been OK. It's business as usual,'' receiver Jordan Westerkamp said. ''Hardie Buck has taken over and is doing a great job. We've come out with a great attitude and have had a positive attitude through the whole thing.''

Receiver is among the Huskers' deepest positions, with Westerkamp and fellow seniors Brandon Reilly and Alonzo Moore taking on additional leadership and helping young players get lined up and understand the offense.

''It's tough,'' Westerkamp said, ''because it's your position coach, specifically for the wideouts. He's a guy out there every single day with you. We're all praying for coach Williams and waiting for him to come back.''

NOTES: QB Ryker Fyfe is set to be fourth-year starter Tommy Armstrong's top backup. Riley said freshman Patrick O'Brien is competing with A.J. Bush for No. 3, though O'Brien could redshirt. ... Freshman Tre Bryant is getting a look as a kick returner. Riley said Bryant ''is in the conversation'' for work at the deep running back position. ... Redshirt freshman Isaac Armstrong, who was invited to join the team after a walk-on tryout last fall, and scholarship freshman Caleb Lightbourn are competing for the punter's job. ''I think it's going to be a pretty good situation,'' Riley said. ... LB Greg Simmons has a sore neck but otherwise is OK after a collision Saturday that required him to be carted off the field.

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Online: AP college football site: http://collegefootball.ap.org