Oksana Grigorieva will file a lawsuit against Mel Gibson alleging -- among other things -- battery, emotional distress and defamation ... TMZ has learned.
Sources tell us Oksana has hired Martin Garbus and Daniel Horowitz ... two formidable lawyers who have been around the block in celebrity cases. Garbus has defended Robert Redford, Al Pacino, and Spike Lee -- and both he and Horowitz rank among America's top litigators.
We're told Garbus and Horowitz will represent almost all things Oksana -- they will be her reps in connection with the domestic violence investigation as well as the extortion probe.
In addition to the civil suit, we're told Garbus and Horowitz will represent Oksana in her music career -- specifically, they will challenge Gibson, who they claim is blocking the release of Oksana's music.
As for the civil battery case against Gibson -- sources tell us the plan is to file it by the end of the year.