BROOKLYN, Mich. -- 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."

A screenshot that appeared to show Gragson's Instagram account liking a meme that mocked George Floyd, a Black man who was murdered by a white police office back in 2020, was circulating around social media on Saturday. It's unclear whether that was the cause of the suspension.

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.

NASCAR fully supports Legacy Motor Club's decision to suspend Noah Gragson. Following his actions on social media, NASCAR has determined that Gragson has violated the Member Conduct section of the 2023 NASCAR Rule Book and has placed him under indefinite suspension.

NASCAR (@NASCAR) August 5, 2023

"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.

The Associated Press contributed to this story.