Ennis' attorney, Stephanie Rickard, told the Sacramento Bee's Matt Barrows that Ennis will say she suffered a swollen lip and ruptured eardrum in an altercation with a woman, not from Foster.
Foster pleaded not guilty last week to felony charges of domestic violence, possessing an assault weapon and forcefully attempting to prevent a witness from reporting a crime.
Police in Los Gatos, California, arrested Foster on Feb. 11 after he allegedly assaulted Ennis. Prosecutors said he struck Ennis eight to 10 times and dragged her by her hair before physically removing her from his home.
Rickard released a statement for Ennis, however, contradicting what Ennis had told police shortly after the alleged assault.
"[Foster] did not strike her, injure her or threaten her," Rickard said, per NBC Sports Bay Area's Matt Maiocco.
Per the police report, "Foster acknowledged breaking [her] phone as well as an iPhone during a previous argument in which he suspected her of secretly recording him," according to Barrows.
Rickard added Ennis and Foster got into an argument following her altercation with the unidentified woman she said caused her injuries. Rickard described Ennis as "extremely upset" and said Ennis told Foster she would "trash his career" if he ended their relationship.
According to Barrows, prosecutors are in possession of a video showing Ennis' fight with the woman.
Foster remains a member of the 49ers but has been away from the team while his case is under investigation. General manager John Lynch said in April that Foster "won't be a part of this organization going forward" if the allegations against him are proven true.