INDIANAPOLIS -- Colts coach Chuck Pagano has been diagnosed with leukemia and is expected to be hospitalized six to eight weeks as he undergoes treatment.

Team owner Jim Irsay made the announcement Monday during a somber and sometimes emotional news conference at the team complex.

"I am optimistic. I feel with every fiber of my body and I know Chuck feels the same way that he can beat this thing," Irsay said.

Offensive coordinator Bruce Arians will serve as the interim coach in Pagano's absence. Irsay said that Pagano requested that Arians coach the team while he is undergoing treatment.

Pagano told ESPN senior NFL analyst Chris Mortensen in a text that he "will be back soon."

Irsay, however, said it was unlikely Pagano would be able to assume full-time coaching duties this year.

"I think it's unlikely he'll be all-in as the head coach the rest of this season," Irsay said. "He may be able to come back and be in the press box or something."

Dr. Larry Cripe, the physician treating the coach at Indiana University's Simon Cancer Center, said Pagano has acute myeloid leukemia, where the bone marrow is producing abnormal white blood cells that interfere with healthy blood cells. Symptoms can include weakness, weight loss and easy bruising or bleeding. Treatments can include chemotherapy, drugs and radiation therapy.

Pagano waited until the Colts' bye week last week to be checked out after experiencing extreme fatigue and bruising, starting in training camp.