"Detectives will thoroughly investigate the case to determine what criminal charges, if any, will be filed and victim services will be offered," police said.
On Thursday, police in the neighboring city of Fort Worth released a report in which officers said Colleen Crowley, 23, told them Manziel hit her several times during an early morning incident on January 30.
Crowley, who lives in Fort Worth, said the 2012 Heisman Trophy winner hit her at an upscale hotel in Dallas and again on the ride to her apartment.
Manziel, reached by TMZ Sports on Thursday, denied hitting Crowley. CNN attempted to reach the Cleveland Browns quarterback Thursday night but was unsuccessful.
NFL player's agent Erik Burkhardt said Friday that he'd dropped Manziel as a client "after several emotional and very personal discussions with his family, his doctors and (Manziel) himself."
"Though I will remain a friend and Johnny supporter, and he knows that 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," he said in a statement.
"His family and I have gone to great lengths to outline the steps we feel he must take to get his life in order," Burkhardt continued. "Accountability is the foundation of any relationship, and without it, the function of my work is counterproductive."
Police: Woman claimed Manziel hit her several times
According to a redacted police report, Crowley told investigators she and Manziel were alone Saturday at an upscale hotel in Dallas after hanging out with friends earlier.
She said Manziel became aggressive and hit her several times, including once on the left ear. She said Manziel insisted on driving her to her apartment in Fort Worth because she was drunk. Manziel hit her again on the drive there, she told police.
The pair went into her apartment and at some point, she fled to a neighbor's place while Manziel reportedly ran away. A neighbor called 911 despite Crowley's objection.
Fort Worth police didn't charge Manziel, 23, saying at the time there was no evidence a crime had been committed in their jurisdiction.
In the Fort Worth report, investigators said some of Crowley's answers were vague, and she became increasingly uncooperative as the interview progressed. She cut off their questioning, saying she didn't want her injuries to be photographed and didn't want to fill out a report.
The Browns said Thursday that the team had nothing more to add to a statement released earlier this week.
On Tuesday, the team said: "We've been clear about expectations for our players on and off the field. Johnny's continual involvement in incidents that run counter to those expectations undermines the hard work of his teammates and the reputation of our organization. His status with our team will be addressed when permitted by league rules."
Many sports media outlets have reported the Browns plan to release Manziel in March.
This marks the latest time that the quarterback, a Heisman Trophy winner as a freshman at Texas A&M University and first-round draft pick with the Browns, has had a run-in with the law.
Another happened October 12 in Avon, Ohio.
In dashcam video, a police officer pulled up to Manziel and a woman -- later identified as his then-girlfriend Crowley -- parked along the side of a two-lane road, telling them about "numerous calls" about their speeding BMW. The woman claimed Manziel hit her several times to prevent her from getting out of the vehicle, while downplaying the incident.
"I don't want to make a big deal," she said.
Crowley later tweeted that "J & I are good" and thanked those who "stopped to check on us and call the police."
"I could see how it may have looked," he wrote. "Anytime anyone sees a guy and a girl arguing on the side of a road they should definitely stop, you never know what that could be. Fortunately, it was just an argument, it was private, and we are all good!"
No charges were filed in that incident. Still, it heightened the spotlight on Manziel, who has been long accused of partying too much and squandering his talents in the process. He went to an alcohol- and drug-treatment center in Caron, Pennsylvania, in early 2015, soon after the end of his rookie NFL season.
"I take full responsibility for my actions, and it's my intention to work very hard to regain everyone's trust and respect," Manziel said after getting out of rehab
. "I understand that will take time and will only happen through what I do and not what I say."
Manziel also was arrested before his freshman season and eventually pleaded guilty to a misdemeanor charge of failing to properly identify himself to police. Counts of possessing a fake driver's license and a charge of disorderly conduct by fighting were dismissed when a judge accepted Manziel's guilty plea.