Peterson said earlier in the day he is "focused" and will play Sunday. He spoke at the team's practice facility while his son, whose name has not been disclosed, was hospitalized in Sioux Falls, S.D.
The Vikings said Peterson was excused from practice Thursday due to a "personal matter," but he returned to the team Friday and told reporters he appreciates the support he has been getting from fans and the Vikings organization and requested his privacy be respected.
"I will be playing Sunday," he said. "I'm ready to roll, focused. Football is always something I fall back on. It gets me through tough times."
The Vikings are at home Sunday against the Carolina Panthers.
Peterson's father, Nelson Peterson, told the St. Paul Pioneer Press Friday the victim is a grandson, but is not Adrian Jr.
"All I can say is, we are asking for prayers and for respect for our family as we deal with this tragic situation," Nelson Peterson said.
Citing multiple sources it did not identify, celebrity website TMZ reported Friday the boy was on life support in a Sioux Falls hospital and hadn't had brain activity since 5:30 p.m. Thursday.
Sioux Falls Police said Joseph Robert Patterson, 27, was charged with aggravated assault and aggravated battery on an infant, and was being held on $750,000 bond Friday.
The (Sioux Falls) Argus Leader said Patterson, who was dating the child's mother, was the only person in the house with the boy when the injuries were inflicted Wednesday. He called 911 around 5:45 p.m. Wednesday to report the boy was choking.
Peterson -- the NFL's 2012 MVP -- is third this season with 421 rushing yards and five touchdowns on 92 carries for the Vikings (1-3).