ESPN NFL analyst Trent Dilfer breaks down why he believes NFL owners cannot take a chance on Johnny Manziel unless they have a solution to his problems off the football field. (1:24)

The Dallas Police Department obtained medical records for Colleen Crowley this week as part of the criminal investigation into whether Johnny Manziel assaulted her, a source familiar with the investigation told ESPN on Thursday.

Crowley filed a complaint Feb. 5 alleging that Manziel assaulted her the night of Jan. 29 and early in the morning of Jan. 30.

Crowley's attorney, Kathy Kinser, told NBC5 in Dallas that Crowley had a ruptured eardrum as a result of the assault. As of a week ago, Crowley could not hear out of her left ear, the source said.

Medical records could verify the injury and could affect any charges that might be filed, the source said.

In Texas, causing serious injury could be considered aggravated assault, which is a felony. The penalty for a conviction for a second-degree felony is two to 20 years in prison and/or a fine of up to $10,000.

Kinser could not be reached for comment.

Dallas police did not immediately return an email for comment. The DPD has said nothing about the investigation since announcing it would take place.

Manziel, who is also being investigated by the NFL for possible violations of the personal conduct policy, spent part of last weekend at the wedding of Mike Evans, his former teammate at Texas A&M.