Megan Fox and Will Arnett are back for the sequel, which also has newcomers such as Arrow star Stephen Amell and Tyler Perry — the latter another brow-raising casting.

Details about Linney’s role are being kept hidden deep in the sewers.

Michael Bay, Bradley Fuller and Andrew Form are producing.

Linney has stayed away from big-studio franchise movies until TMNT 2, but the actress, now a new mom with a 1-year-old under her belt, is becoming open to projects that are geared toward younger audiences.

Her more recent movies have been a mix of period pieces and dramas, ranging from Hyde Park on Hudson to The Fifth Estate. She is currently onscreen opposite Ian McKellen in Mr. Holmes and also has the all-star 1920s literary drama Genius — with Colin Firth, Guy Pearce, Jude Law and Nicole Kidman — in the can.

Linney is repped by ICM Partners, Brillstein Entertainment Partners and Morris Yorn.