Arkansas football coach Bobby Petrino was placed on administrative leave Thursday night after apologizing to his wife, his family and the university for not earlier admitting that a 25-year-old woman was riding with him when he crashed his motorcycle Sunday.

He said he had been involved in an "inappropriate relationship," which is why he had previously not identified the woman -- football program assistant Jessica Dorrell.

"My concern was to protect my family and a previous inappropriate relationship from becoming public," the 51-year-old father-of-four said in a statement.

"I've acknowledged this previous inappropriate relationship with my family and those within the athletic department administration.

"I apologize to my wife, Becky, and our four children, Chancellor [David] Gearhart, Jeff Long, the Board of Trustees, University administration, my coaching staff, student-athletes and the entire state of Arkansas."

The statement was released prior to a press conference held by Arkansas Athletic Director Jeff Long, who said the coach would be on paid administrative leave until he had conducted a review into the circumstances surrounding Petrino's accident.

"I expect to move very expeditiously in my review of this personnel matter and hope to have a resolution soon," Long said, adding that he did not know yet if Dorrell would also be suspended from her position at the university.

Long said that assistant head coach Taver Johnson would act as head coach in the interim.

Despite saying he was "disappointed" and "surprised" Petrino did not inform him of the full details of the crash until Thursday, Long said he had not yet made any conclusions about how he would respond to the matter.

"I am disappointed Coach Petrino did not share with me, when he had the opportunity to, the full extent of the accident and who was involved," he said.

Earlier Thursday, police said Dorrell was with Petrino when he crashed his motorcycle.

Dorrell, a former Arkansas volleyball player, was recently hired to serve as the student-athlete development coordinator for football. Police said it was Dorrell -- unharmed in the accident -- who flagged down a passing motorist after the wreck.

A police report, obtained by the Arkansas Times, says the two were picked up by the motorist and "upon arrival at the intersection of East Huntsville Road and Crossover Road in Fayetteville, Passenger Dorrell departed in her personel [sic] vehicle."

In a statement issued following the accident, the university said, "Petrino was involved in a motorcycle accident on Sunday evening that involved no other individuals."

The head football coach also failed to mention he had a female passenger during a Tuesday news conference after he was released from the hospital.

"When I came out of a ditch, there was a lady there that had flagged down a car," Petrino said Tuesday.

He also revealed he was not wearing a helmet, and said he considered himself lucky to have survived. He suffered a cracked vertebrae, four broken ribs and displayed a visible case of road rash on his face.

Petrino is entering his fifth season as coach of the Razorbacks, with the team going 21-5 over the past two seasons.

Prior to arriving at Arkansas, Petrino had a successful run at Louisville and a brief stint as head coach of the Atlanta Falcons in 2007.