Billy Gillispie has resigned as Texas Tech's basketball coach, the school announced Thursday.
Gillispie, who was Tech's coach for just 18 months, left because of health reasons. He was twice hospitalized in recent weeks, and he visited the Mayo Clinic last week for symptoms that seemed to be related to stress.
However, he was also being investigated by the school amid allegations of player mistreatment and possible violations of NCAA rules regarding practice time.
"Billy has decided to focus on his health and we wish him a full recovery," Tech athletic director Kirby Hocutt said in a statement. "We are proud of the young men that he has brought to this campus. Billy's decision allows him to concentrate on his well-being and allows us to turn our attention to preparations for the upcoming season."
Chris Walker, who was placed in charge of the program's day-to-day operations last week, will act as head coach until an interim coach can be named for the 2012-13 season, according to the statement from Tech.
Last week, Gillispie, 52, was treated at the Mayo Clinic in Rochester, Minn., for abnormal headaches, kidney problems and high blood pressure, according to the Lubbock Avalanche Journal. He had been ordered by doctors to avoid stressful environments for at least 30 days.
Tech officials announced on Aug. 31 they were looking into Gillispie's leadership as a coach as a result of a meeting between Hocutt and a group of Tech players. The players had concerns about the way they were being treated by Gillispie.
An unnamed player told ESPN.com that the players' concerns focused on "a lot of stuff that goes on in practice, everything within the program, the way we're being coached, the relationship we've got with our coach, practice hours and stuff like that."
Hocutt revealed Tech self-reported secondary NCAA violations in January stemming from practices last fall that exceeded allowable time limits.
Gillispie was given a written reprimand and was told there would be "zero tolerance for further disregard for the rules," Hocutt told the Avalanche Journal.
Hocutt had planned to meet with Gillispie regarding the new concerns, but Gillispie was admitted to the University Medical Center on Aug. 31 after suffering severe pain and what he told the Avalanche Journal felt like a stroke or heart attack.
In Gillispie's only season at Texas Tech, the Red Raiders went 8-23 overall and 1-17 in the Big 12.
He had been fired at Kentucky after going 22-14 and failing to reach the NCAA Tournament in 2008-2009.