The father-in-law of disgraced Tour de France winner Floyd Landis has committed suicide, police said.

David Witt, 57, the stepfather of Landis' wife, Amber, died on Tuesday of a self-inflicted gunshot wound to the head, San Diego Police said.

"The Landis family is devastated by the news of David's death," said Michael Henson, a spokesman for Floyd Landis.

"They loved him dearly and they miss him. They hope that their privacy is respected in this time of mourning."

Police said Witt, of La Mesa, California, was discovered at 3.05 p.m. in a parking structure in the North Park section of San Diego.

He was rushed to hospital but died of the single gunshot wound seven hours after he was found.

Landis captured the prestigious Tour de France last month but ultimately tested positive for abnormally high levels of the male sex hormone testosterone.

Witt, a San Diego restaurant owner with his wife Rose, was at the finish line in Paris when Landis won the race.

Police said they were unaware of any suicide note left by Witt.