Tissue from Junior Seau's brain was taken to the National Institutes of Health for researchers to study possible head injuries sustained by Seau during his 20-year NFL career, the San Diego Union-Tribune reported Thursday.

Seau's oldest son, Tyler, and estate trustee Bette Hoffman signed the release that allowed the San Diego County Medical Examiner to deliver brain tissue to the NIH's National Institute of Neurological Disorders and Stroke in Bethesda, Md., about two weeks ago, according to the report, which relied on unnamed sources.

The NIH issued a statement that read, "The National Institutes of Health (NIH) is not directly involved in an analysis of former NFL player Junior Seau's cause of death, but physicians at NIH's National Institute of Neurological Disorders and Stroke conduct research on traumatic brain injury and have agreed to carry out an analysis of the autopsied tissue. In order to protect Mr. Seau's children's right to privacy, NIH will not discuss the status of the tissue or any subsequent findings."

Concerns about the long-term effects of concussions and head injuries in football have escalated in recent years.

Seau, 43, committed suicide on May 2, Whether head injuries Seau may have sustained contributed to depression and his suicide remains unclear.