The phrase "direct collaborator" is correct and usable in written English.
You could use it when referring to someone who is working with you in a close working relationship, such as a business partner or team member. For example, "My direct collaborator on this project has been essential to our success."
In our field, it is not unusual for researchers initially to distribute a unique strain of an organism only to direct collaborators.
Raphael's "Strangers" film, which he directed with collaborator Felix Lajeunesse, puts viewers in the studio with Watson such that when the musician turns to look at you, you almost want to say something to him.
The music video for "Te Amo" was shot over two days on April 29 and 30, 2010, in Vigny, France and was directed by longtime collaborator Anthony Mandler, who had previously directed the music videos for "Wait Your Turn" and "Russian Roulette".
His feature film Holding the Man – his first since 2006's Candy, starring Heath Ledger – will close the 2015 Sydney film festival, and in November he will direct long-time collaborator Geoffrey Rush in King Lear for the Sydney Theatre Company.
Deborah Warner directs her frequent collaborator Fiona Shaw in "The Testament of Mary".
My days therefore frequently contain meetings with members of my direct team, scientific collaborators, clinicians or pharmaceutical companies from all over the world.
Deborah Warner directs her frequent collaborator Fiona Shaw in "The Testament of Mary". Shaw portrays an impassioned Virgin Mary, who ruminates on her son's death twenty years after the fact.
The Second Coming was a project in 1982, part concert film, part feature film, to be directed by Devo collaborator Chuck Statler.
Leon Botstein, Bard's president, conducts his adventurous American Symphony Orchestra and a largely Russian cast; Thaddeus Strassberger, a frequent Bard collaborator, directs.
Nottage is now working on a companion piece to Sweat, which began life at the Oregon Shakespeare festival directed by longtime collaborator Kate Whoriskey.
