Adrian Peterson, already facing felony charges in Texas for child abuse, was accused in a separate incident involving another son who was 4 years old, KHOU-TV in Houston has reported.
They're allegations the Minnesota Vikings running back's lawyer says were unfounded and more than a year old.
The CBS affiliate KHOU cited text messages that reportedly include a photo of the son with an apparent head wound covered by bandages.
The Houston TV station reported the mother of the 4-year-old -- from a different mother than the child he stands charged with abusing -- filed a report with Child Protective Services but no charges were brought.
Peterson attorney Rusty Hardin said in a statement that the accusation was more than a year old and that "authorities took no action."
"An adult witness admittedly insists Adrian did nothing inappropriate with his son," Hardin said in the statement to media.
The Vikings released a statement Monday night, saying they would "defer any further questions" from the media regarding the accusations to Hardin.
"As part of the information we have gathered throughout this process, we were made aware of an allegation from 2013 in which authorities took no action against Adrian," the Vikings said in the news release.
The reported text exchange was as follows, according to KHOU-TV:
Mother: "What happened to his head?"
Peterson: "Hit his head on the Carseat."
Mother: "How does that happen, he got a whoopin in the car."
Peterson: "Yep."
Mother: "Why?"
Peterson: "I felt so bad. But he did it his self."
According to the report, Peterson then goes on to say he was disciplining his son for cursing at a sibling, though how specifically the child was wounded wasn't made clear.
Mother: "What did you hit him with?"
Peterson never directly answered, the report said, but later replied: "Be still n take ya whooping he would have saved the scare (scar). He aight (all right)."