Revelations in recent years that thousands of former football players might have severe brain trauma from injuries sustained on the field have set off a rush in the medical community to seize the potentially lucrative market for assessing brain damage. But experts say claims regarding the validity of these assessments are premature and perhaps unfounded.

Most researchers believe that C.T.E., or chronic traumatic encephalopathy, the degenerative brain disease found in dozens of former N.F.L. players, can be diagnosed only posthumously by analyzing brain tissue. Researchers at U.C.L.A. have developed a test they assert might identify the condition in a living person by injecting a compound that clings to proteins in the brain and later appears in a PET scan. But some are skeptical.

“There has really been so much hype surrounding C.T.E., so there is a real need for making sure the public knows that this type of science moves slowly and must move very carefully,” said Robert Stern, a professor of neurology and neurosurgery at Boston University School of Medicine and a founder of the Center for the Study of Traumatic Encephalopathy. He is part of a group that is developing a different biomarker to identify tau, the protein that is a hallmark of C.T.E.

“My fear is the people out there who are so much in need, scared for their lives and desperate for information, it might give them false hope,” he said.