Antonio Smith's child abuse investigation is not only sexual in nature ... TMZ Sports has learned the alleged victim is one of his relatives.
We broke the story ... the Fort Bend County Sheriff's department in Texas has been investigating the Denver Broncos' new defensive end since late last year.
Now, a family source tells us the accuser told investigators the alleged abuse involved repeated sexual contact from December 2010 through January 2014. We're told the accuser is related to Smith, but not an immediate family member.
According to our source ... the alleged victim also told investigators about a conversation when Smith told her, "God has a plan," and "some relationships are meant to go deeper than just blood lines."
We're told all the alleged incidents occurred at Smith's home outside Houston. He played for the Texans from 2009 to 2013.
No charges have been filed against Smith. A Broncos rep says the team is gathering information. We've reached out to Smith, but so far ... no response.