Manning has thrown thousands of perfect passes in NFL games, but it's his latest medical Hail Mary that is causing controversy. Out for months with a bulging disc in his neck, Manning reportedly traveled to Europe for experimental adult stem cell therapy, that some say is dangerous.
"When you leave a well regulated environment, all bets are off," said Dr. Lawrence Goldstein, director of the University of California-San Diego stem cell program.
In treatment that is not approved by the FDA, stem cells are harvested from a healthy part of your body, and then injected into the problem area. The hope is, they can repair damaged cells, but the problem, some doctors say, is that there is not enough proof it works for this type of injury.
"The downside is that many people might be hurt by subjecting themselves to a risky procedure, or procedure with unknown risks, when there is no evidence of benefit to be gained," Dr. Goldstein said.
Manning is one of football's megastars. He is clearly desperate to get back on the field. Before the season, he said, "To say I am disappointed in not being able to play is an understatement...I am doing everything I can to get my health back."
It doesn't appear that Manning's stem cell treatment was as successful, but doctors worry.
"If hundreds or thousands of people then go out and say 'Oh well, it's good enough for Mr. Manning, what about me?'" Dr. Goldstein said.