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.
Pagano believed he was experiencing football fatigue, but a blood test early last week revealed the diagnosis of leukemia.
The initial phase of treatment usually requires a hospital stay of four to five weeks, though Irsay later acknowledged he expected Pagano to be in the hospital at least six weeks.
Cripe said Pagano began the "arduous" treatment last week and that many adults do recover from the disease. For now, Pagano is being kept in a "protected" hospital environment where air is filtered and hand-washing is essential.
Pagano was admitted last Wednesday evening; the team had a bye this weekend and players and the assistants, other than Arians, were not told Pagano was ill until Monday morning.
Cripe said that Pagano is handling the chemotherapy treatments well so far. The goal of the treatment is to "cure" Pagano, which means the disease remains in remission for 3 to 5 years.
Cripe said Pagano's wife, Tina, had been at his bedside each night. Irsay said she was the one who pushed him to see the doctor after noticing unusual bruising on his body.
Arians was notified of the illness in a phone call with Pagano; players and the other assistants didn't find out until Monday -- another blow for a team that has faced more than its share of adversity over the past decade.
"He will do fine," Arians said, his voice cracking as he recalled his own fight with prostate cancer in 2007. "I know him. He's a fighter. He's survived tough times already in his life. As a cancer survivor myself, I know that these first few days are really hard on you but as he and I talked yesterday, it's just a matter of time."
It didn't take long for the Colts to figure out how to pay tribute to the first-time head coach who rekindled excitement in the locker room and around town after the Colts' awful 2-14 season a year ago.
"I asked Mr. Irsay if we would leave the light on in his office permanently till he comes back and we are going to do that," Arians said.
General manager Ryan Grigson said he was not yet certain how the rest of the coaching duties would be split up, though he expected all of the assistants to pitch in.
Pagano, who turns 52 on Tuesday, was hired in January after serving as the Baltimore Ravens' defensive coordinator.
"He's going to be greatly missed, there's no question about it in terms of his intensity, his energy, his leadership, the things that made him the candidate that (general manager) Ryan (Grigson) and I selected ultimately as our head coach," Irsay said. "I know in meeting with the team, in meeting with the coaches, there's nothing more than we want to get that Green Bay game ball and have a victory game ball and be able to walk that into the hospital and put that in his hands. That's our goal."
Pagano earned his first win Sept. 16 against the Vikings. The Colts (1-2) had a bye last weekend.
"This is not an easy day for all of us," said Arians, a longtime NFL assistant who has never been a head coach. "Not the way that I had ever dreamed about addressing a group like this. But I know we are going to get through it."
The Colts have no doubts Pagano will win the battle.
"We are very optimistic. Chuck is a fighter," Grigson said. "As we talked to the players this morning, the best medicine for him is for the team to continue to fight four quarters and to show him what he said is still in existence and it will be."
Information from ESPN senior NFL analyst Chris Mortensen and The Associated Press was used in this report.