Sky News quoted Daniels as saying that both he and other officials from Athletics South Africa did not tell the 18-year-old that she was being tested because of queries over her gender.
"I'm so sorry for the part I played; because of my negligence she went through all that," Daniels, who quit his post at the weekend, said.
He also said the athlete was not briefed by officials when the story made headlines around the world.
The coach, who has worked with Athletics South Africa since 1993, also revealed that he had personally apologized to Semenya for what he described as the "repulsive" handling of her case.
He said she told him that she did not blame anyone.
Semenya was ordered to undergo gender testing shortly before her victory in the women's 800 meters at the World Athletics Championships in Berlin last month.
The sport's ruling body, the The International Association of Athletics Federations, demanded clarification after dramatic improvements in her performance over the past year.
The controversy provoked outrage in South Africa, where Semenya was given a "heroine's homecoming" when she returned to Johannesburg airport after her gold medal win.
The head of the ASA, Leonard Cheune, has consistently denied suggestions that the sporting body failed in its duty to protect the teenage athlete.
The results of the gender test have not yet been revealed.