CHICAGO (AP) -- Illinois-Chicago coach Jimmy Collins was admitted to the hospital Wednesday after tests showed he had suffered an abdominal aortic aneurysm, university officials said.

Illinois-Chicago basketball coach Jimmy Collins, left, shares a laugh with former forward Elliot Poole. (AP Photo/Charlie Riedel)

Collins, 59, gave notice of an indefinite leave of absence late last month because of "physical and mental" exhaustion. Neither Collins nor the university knew of his medical condition at that time, school spokesman Mike Cassidy said Wednesday night.

Results from medical tests performed last week showed Collins had suffered an abdominal aortic aneurysm, which is swelling of the main blood vessel -- the aorta -- in the abdomen. The abdominal aorta carries blood from the heart to the abdomen, pelvis and legs. After an aneurysm, the blood vessel wall thins and is in danger of rupturing.

Collins was scheduled to have surgery on Thursday morning to repair the aortic artery at the University of Illinois Medical Center, Cassidy said.

Associate head coach Mark Coomes has led the Flames since Collins announced his leave of absence Dec. 23.

Collins has said he decided to go on leave after the team played Dec. 21 at Penn, in part because he felt staying with the team "was causing unneeded stress."

No time has been set for when Collins will return, Cassidy said.

"He'll be on continued leave until he completes a full recovery," Cassidy said. "He'll decide when he's fully recovered."

Before he took over at Illinois-Chicago in 1996, Collins was an assistant coach at Illinois.