The Santa Clara District Attorney’s office will not file domestic abuse charges against San Francisco 49ers defensive end Ray McDonald stemming from his Aug. 31 arrest.

Prosecutors said they were unable to charge McDonald partly because of a significant lack of cooperation by the alleged victim, McDonald’s fiancee.

“Conflicting versions of the event, a lack of verifiable eyewitnesses and a significant lack of cooperation from Jane Doe, we cannot prove a crime occurred,” Lindsay Walsh, Santa Clara Deputy District Attorney in charge of the case, said in a statement released Monday. “In this particular case, there were particular pieces of information missing.”

The decision concludes a nearly 10-week investigation of the defensive lineman by San Jose police detectives and prosecutors from the District Attorney’s office.

McDonald was arrested in the early morning hours of Aug. 31 on suspicion of domestic violence while celebrating his 30th birthday at his home with teammates and friends. Police said the alleged victim had “visible injuries.” McDonald lives at the home with his fiancee. McDonald was later released on $25,000 bail.

Walsh said McDonald was cooperative with officers on the night of the incident and gave a follow-up interview later.

“I am confident in our decision,” Walsh said. “We really don’t know what happened between the two parties.”

A portion of a 911 call was leaked following McDonald’s arrest.

“Her fiance was hitting her,” the unidentified caller said. “He was trying to pull her out of the house. She’s 10 weeks pregnant and refusing medical.”

McDonald continued to practice and play with the team since the incident as 49ers coach Jim Harbaugh, general manager Trent Baalke and CEO Jed York said they would allow “due process” to play out.

McDonald was drafted by the 49ers in the third round in 2007. He has played in every one of the 49ers’ games this season and has 24 tackles.

The issue of domestic violence among NFL players came to the forefront after a second video showed former Baltimore Ravens running back Ray Rice striking and knocking out his then-fiancee and now-wife, Janay Rice, in the elevator of an Atlantic City casino. Rice was originally given a two-game suspension by commissioner Roger Goodell, who later responded to the public firestorm by suspending Rice indefinitely. Rice has appealed and a decision from Judge Barbara Jones is expected before Thanksgiving.