The actor - who played Charlie in the HBO show - has left after reportedly falling out with the creator as they began work on season three.
A source told the New York Post's Page Six: ''They've just started work on season three, and Chris is at odds with Lena. He didn't like the direction things are going in, which seems a bit odd since the show put him on the map.''
However, Christopher's representative insists he left 'Girls' in order to focus on ''other projects''.
The representative said: ''[Chris] is grateful for the experience of collaborating with Lena, Judd[Apatow], and the entire 'Girls' cast and crew, but right now he's working on numerous other projects and has decided not to return to the show.''
Lena recently revealed she is excited about season three and wants to extend its run from 10 to 12 episodes.
She said: ''We're starting season three at the end of March. I'm so excited.
''I would love that [to have 12 episodes instead of 10] I think that a little more would be just a little more storytelling real estate, and it would be amazing. But you know, so I shoot four-and-a-half months out of the year, then I'm editing, then I'm doing press, then I'm writing, then I'm back.''
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