Dallas police said they received a complaint of the assault Friday that occurred January 30 and initiated the investigation.
Earlier Friday, Manziel was ordered that he must stay away from his former girlfriend for two years. That's according to a protective order signed by a judge.
Manziel, 23, is also to pay $12,500 in legal fees and isn't allowed to own a firearm.
Earlier today, we learned Manziel's agent dropped him.
"It is with deep regret that, after several emotional and very personal discussions with his family, his doctors and my client himself, I have made the decision to terminate my professional relationship with Johnny Manziel," agent Erik Burkhardt said in a statement.
"Though I will remain a friend and Johnny supporter, and he knows I have worked tirelessly to arrange a number of professional options for him to continue to pursue, it has become painfully obvious that his future rests solely in his own hands," Burkhardt said. "His family and I have gone to great lengths to outline the steps we feel he must take to get his life in order. Accountability is the foundation of any relationship, and without it, the function of my work is counterproductive.
VIDEO: Manzie's agent dumps him
Manziel's father, Paul, told the Dallas Morning News that Manziel has refused to enter area rehab facilities twice in the past week. He said the family tried to get Manziel to enter a local addiction facility on Saturday, but Manziel refused to stay. Paul Manziel said he tried to have his son admitted to a psychiatric and chemical dependency hospital on Tuesday, but Manziel was allowed to leave even though his father told officers that he believed Manziel was suicidal.
The first attempt to get Manziel to enter rehab, his father told the newspaper, was Saturday afternoon after news surfaced of a police investigation into an alleged incident between Manziel and his ex-girlfriend the night before. According to the police report,Manziel and his ex-girlfriend were at a hotel in downtown Dallas and left together after he struck her. The ex-girlfriend told officers that she and Manziel shouted angrily at each other and that he struck her several more times on the drive to her apartment in Fort Worth, Texas.