Shares of Chipotle Mexican Grill (CMG) - Get Report are lower on Monday morning, following reports that hedge fund manager Bill Ackman's Pershing Square Capital filed a prospectus with the SEC to sell 2.88 million shares.

That is equal to a 10% stake in the fast casual Mexican food restaurant chain. Pershing doesn't have plans to immediately divest its interest, but is reserving the right to do so later.