1
general::
1. Keep undecided or unscheduled, as in We don't know how much fabric will be needed; let's leave that open, or The doctor leaves Fridays open for consultation. This expression uses open in the sense of "undetermined," a usage dating from the mid-1500s. 2. leave oneself open. Remain vulnerable to; also, remain willing to consider. For example, Her actions left her open to widespread criticism, or I left myself open to further suggestions about how to proceed. Also see under LAY OPEN.
American Heritage Idioms
2
general::
Phrase(s): leave something open
to leave a date or time unscheduled. • I left something open on Friday, just in case we want to leave work early. • Please leave an appointment open for Mrs. Wallace next week. She will be calling in to our office for an appointment.
McGrawhill's American Idioms And Phrasal Verbs