20th Century Fox is taking Gambit off the schedule but adding two mystery movies in 2017 and 2018, according to Collider. These two new movie slots are reportedly for October 6, 2017 and January 12, 2018, but no new release date has been stated for the Channing Tatum-starring Gambit.
20th Century Fox's Gambit had some delays which led to original director Rupert Wyatt dropping out; Tatum and the film's producers eventually landed Bourne Identity director Doug Liman to replace him, but with the filming not said to begin until March 2016, meeting it's original October 7, 2016 release date seemed unlikely.
As for the reported two new mystery Marvel movie slots announced by the studio, there are several potential options ranging from Gambit to a Deadpool sequel. Fox has two other films announced with no release date as of yet, however: New Mutants and X-Force, the latter of which Deadpool's leading man Ryan Reynolds called a "priority" after his film's success.