CHICAGO (CBS) — Cardinal Francis George said he’s asked the Roman Catholic Church to begin searching for his successor as archbishop of Chicago, because of his ongoing treatment for cancer.

“The fact that my health is uncertain; it isn’t just a question of imminent death. I’m not going to be dying, I don’t think, in the next few months; but it’s a question of being able to spend your entire energy on what is my responsibility as archbishop of Chicago,” the cardinal said Friday morning, as he discussed the upcoming canonizations of Pope John Paul II and Pope John XXIII.

He said chemotherapy saps the energy he needs to do his job as head of the Chicago archdiocese.

“It’s something you have to pay attention to full-time, and now it looks as though I’m going to have to be spending a little more attention on my health,” he said. “So it’s just not fair to the Archdiocese to have someone who may not be able to do the job as well as I believe it should be done.”

The 77-year-old cardinal also said a weakened immune system from chemotherapy will keep him from visiting Rome for the April 27 canonizations.

George said the formal process of selecting his replacement has not started, but will begin soon.

Last month, the cardinal was hospitalized for a week after suffering an infection from his latest round of chemotherapy.

He started his latest treatments for cancer in mid-Mrach, after doctors found fresh signs of cancer in his right kidney. It’s his third bout with cancer; he underwent treatment for kidney cancer two years ago, and had his bladder removed in 2006 after he was diagnosed with bladder cancer.

George already has submitted his resignation to the Pope, as all cardinals must do when they turn 75, but like many cardinals, was being allowed to stay on past his 75th birthday.

No timetable has been given for picking George’s successor.