1
general::
Phrase(s): leave the door open (for something)
Fig. to provide for the possibility that something might happen. • I think that the matter is completely settled, although we have left the door open for one or two last-minute changes.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Allow for further action or discussion. For example, This will's terms leave the door open for fighting among the heirs. This metaphoric expression transfers the invitation implied by an open door to future events. Also see OPEN THE DOOR TO.
American Heritage Idioms