STATE COLLEGE, Pa. -- The new football coach at Penn State could be announced "in a matter of days rather than weeks" as a national search is underway, Nittany Lions athletic director Dave Joyner said Thursday.

The university confirmed Thursday that Bill O'Brien will leave to become coach of the Houston Texans.

Joyner said a "number of prominent head coaches" have reached out to Penn State, although he declined to mention names or whether any interviews had been conducted. He also said past Penn State ties are not required of the next coach, but they will be considered.

"Our job is going to be to select the next great football coach at Penn State and to get the best football coach available," Joyner said. "We've begun a very robust search that will bring us a great next football coach."

Until a hire is made, longtime defensive line coach Larry Johnson will serve as interim coach. He will be primarily charged with recruiting duties and keeping the current class together, but Joyner wouldn't rule out the assistant becoming the permanent coach if he expressed interest.

Penn State athletic director Dave Joyner feels Bill O'Brien left the program in better shape than he found it, and says of the PSU job, "It's different in that I think it's a lot more attractive at this point." Abby Drey/Centre Daily Times/MCT/Getty Images

Johnson is the only remaining assistant from Joe Paterno's tenure and has coached in Happy Valley since 1996. It is not yet known which PSU assistants might follow O'Brien to Houston.

"I'm humbled by the confidence that Penn State has bestowed upon me during this critical time for the football program and honored to do my part to help Penn State," Johnson said in a news release. "My job will be made very easy since we have a team comprised of tremendous student-athletes, coaches, trainers and support staff who are second to none and care as much about Penn State as I do."

Joyner, who will lead a six-person search committee, said program stability is a priority and that finding a coach who plans to stick with Penn State will be important.

Still, he believed O'Brien left the program in better shape than when he found it.

"I think the atmosphere around this search is very much different than the last search," Joyner said. "It's different in that I think it's a lot more attractive at this point."

O'Brien saw the team through unprecedented sanctions, levied by the NCAA in response to the Jerry Sandusky child sex-abuse scandal, and led Penn State to back-to-back winning seasons of 8-4 and 7-5.

Most players contacted by ESPN.com were surprised by the move -- but all wished O'Brien well.

"He came into a position that was hard for his family, with the sanctions that we got," wideout Geno Lewis told ESPN.com. "You have to look at what he did and how he did all he could. You can't really be mad at him for leaving after two years. I still really respect him."

Joyner said he and O'Brien were in contract discussions for weeks before the coach received an offer from the Texans he couldn't refuse.