In most adult cases, hGH deficiency would be caused by either a tumor or some other malfunction of the pituitary gland or by the treatment (such as radiation) of a malfunctioning pituitary gland, Wadler said.

"It is not common; it is rare," Wadler said. "But it is real."

He would not speak specifically on the validity of Segui's case, but said: "You wouldn't expect it in an athlete because elite athletes cannot perform at an elite level if they have hGH deficiency or at least you wouldn't expect that they could. ... Having said all of that, he may have had a head injury or a pituitary tumor and didn't tell anybody about it. We don't know."

Wadler added, however, that doctors normally would not test for a hGH deficiency and then offer treatment. Instead, there should be an investigation into what is causing the deficiency including evaluating the patient's history and physical exams that could include magnetic resonance imaging tests before making a diagnosis.

"It's not just a matter of treatment. You need to know what caused it," Wadler said. "It's not just a matter of, `It happened.'"

Orioles strength and conditioning coach Tim Bishop said Segui never told him he was taking hGH.

"Obviously, there are people in this world who are deficient of growth hormone, but I certainly don't know David Segui's personal health history," Bishop said.

He added that Segui had every right to keep private his dealings with a personal physician.

"He was a great worker," Bishop said of Segui. "He trained almost every day and was very in tune with his body. Just a great athlete who trained very hard, took it very seriously."

Lopez said he had never heard fellow players talk of using hGH legally or illegally.

"I don't know how they get it, how they use it," he said. "To me, it's something I'm not very familiar with. I don't know how they get it. I've read a little bit, but besides that, I never heard anybody in the clubhouse talk about using it."

Sun reporters Jeff Zrebiec and Dan Connolly contributed to this article.