Harrison was arrested Saturday after hitting 29-year-old Beth Tibbott at her home in Ohio Township, according to a police affidavit.
Harrison, of Franklin Park, was arraigned on charges of simple assault and criminal mischief. The 29-year-old was released on his own recognizance pending a preliminary hearing Thursday.
On Monday, Harrison apologized for the fight through his lawyer.
"I initially told him that my advice was he not speak with any of the media nor that I speak with any of the media, and he felt strongly that I convey his contrition and his regret regarding the incident," Harrison's lawyer, Bobby Del Greco, told the Pittsburgh Tribune-Review on Monday.
The couple had been arguing before just before 1 p.m. when Tibbott locked herself in a bedroom, the police said.
While Tibbott was trying to call 911, Harrison broke down the door, took her cell phone and broke it in half, according to police. Tibbott said Harrison then hit her across the face with an open hand and knocked off her glasses.
Police said Tibbott had "red marks" on her left cheek. She had called them after the alleged assault, saying she was afraid of Harrison.
Harrison drove from the house in a Hummer and was pulled over minutes later by Franklin Park police. Police said Harrison corroborated her account of the incident, according to several Pittsburgh-area media outlets.
Harrison was arraigned, then released on his own recognizance pending a preliminary hearing at 8:30 a.m. Thursday.
Steelers spokesman Dave Lockett said the team is gathering information, but considers the charges a personal matter of Harrison's. The player's agents also declined comment.
The Steelers linebacker had career highs of 98 tackles and 8½ sacks last season. He was signed by Pittsburgh in 2002 as a rookie free agent out of Kent State.
Information from The Associated Press was used in this report.