Colts quarterback Peyton Manning underwent a stem cell treatment in his neck in Europe, according to a Fox Sports report, a procedure that is not approved in the United States yet.

According to Fox Sports, Manning took a private jet to Europe to have the treatment in which doctors took fat cells from his belly probably, put it in a culture and inject them in his neck, hoping that the cells will regenerate the area and the nerves.

Colt's head coach Jim Caldwell declined to comment on Manning's health situation, according to CNN.

The medical community in the U.S. have cautioned against undergoing treatments abroad because they are merely "experimental", they are unregulated and it is not known if they have serious side effects, CNN reports.