BROOKLYN, Mich. (AP) — Driver Noah Gragson has been suspended indefinitely by NASCAR and Legacy Motor Club due to undisclosed activity on social media.

“I am disappointed in myself for my lack of attention and actions on social media,” Gragson posted Saturday. “I understand the severity of this situation. I love and appreciate everyone. I try to treat everyone equally no matter who they are. I messed up plain and simple.”

Grant Enfinger will be in the No. 42 Chevrolet, making his Cup debut in Sunday’s race at Michigan International Speedway to replace Gragson.

NASCAR said Gragson violated the member conduct of its rule book without providing details.

“His actions do not represent the values of our team,” Legacy Motor Club said in a statement.

The 25-year-old Gragson, who is from Las Vegas, is in his first full season in the Cup series and is No. 33 in points.