The two-year-old son of Minnesota Vikings star running back Adrian Peterson died from injuries received in an alleged beating, US media reported.
Police in Sioux Falls, South Dakota, said a two-year-old boy died from injuries Friday sustained in an assault on Wednesday but did not name the child.
However, Peterson's father, Nelson Peterson, told the St. Paul Pioneer Press that the boy was his grandson.
Peterson himself thanked fans and fellow players for their support in recent days, although he declined to discuss specifics.
"I really appreciate all the support that I've been receiving from fans, the Vikings organization," Peterson said.
"This is a private matter and I would ask you all to please just respect my privacy and not ask at all about the situation at hand. Thanks."
The Vikings said on their website that Peterson had rejoined the team on Friday after traveling to South Dakota to deal with a private matter.
Prior to the boy's death, Joseph Robert Patterson, 27, had been arrested on two counts of aggravated domestic assault and aggravated battery of an infant, court documents showed.
Patterson was being held on $750,000 cash bond police said.
Police said they were called to Patterson's apartment on Wednesday where they found the two-year-old boy unresponsive. Doctors later determined his injuries were consistent with abuse.
The boy had recently moved to the home with his mother.
Patterson has a history of domestic abuse against his own son and the boy's mother, also from Sioux Falls, the paper said, citing court records.
Peterson, who holds the record for the most rushing yards in a single National Football League game with 296, said he would still be playing for the Vikings on Sunday against Carolina.
"I will be playing Sunday ... without a doubt," said last year's league MVP.
Peterson also used Twitter on Friday to reiterate his thanks to "my family, my fans and fans of other teams for their support."
"The NFL is a fraternity of brothers and I am thankful for the tweets, phone calls and text messages from my fellow players," he said.
Peterson has been selected to the Pro Bowl game five times and won two NFL single season rushing titles in 2008 and 2012. The Vikings' seventh overall pick in the 2007 entry draft, he was named MVP of the Pro Bowl game in 2007.