Colts Coach Chuck Pagano is undergoing treatment for a form of leukemia. (Michael Hickey / AP)

Updated at 10:43 a.m. with owner Jim Irsay confirming diagnosis

Indianapolis Colts Coach Chuck Pagano is battling a treatable form of leukemia and it is unlikely that he will be able to fully return to coaching this season.

Colts owner Jim Irsay made the announcement this morning, confirming Indianapolis Star and ESPN reports that Pagano has acute promyelocytic leukemia. Pagano, who turns 52 on Tuesday, has been hospitalized since Wednesday. He had been feeling fatigued since training camp and underwent blood tests during the team’s bye week.

“It’s been a very difficult week,” Irsay said (via the Indianapolis Star). “… 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.”

In the short term, the Colts are preparing for Pagano to miss most of the rest of the season, naming offensive coordinator Bruce Arians  the interim coach. “It is unlikely [Pagano] will be all-in as a head coach this season,” Irsay said.

Pagano’s doctor, Larry D. Cripe, called the process of Pagano’s treatment, “long and complicated.” Pagano has been receiving chemotherapy and, Cripe said, has done well so far.

Pagano is expected to be hospitalized for four-to-six weeks and, Irsay said, was “disheartened that the NFL Network” wasn’t available in his room. “We talk about how grabbing the Lombardi Trophy,” Irsay said, “one day is going to be that much sweeter when we overcome this.”

Pagano is in his first season as coach of the 1-2 Colts after serving as the Baltimore Ravens’ defensive coordinator. The Colts host the Green Bay Packers on Sunday.

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