Albion boss Mark McGhee has followed predecessor Steve Coppell's lead by bringing the highly-rated young keeper to Withdean, after being hit by a knee injury to Ben Roberts.
England scouts have been tracking Flitney's progress and the temporary switch will give the 19-year-old another chance to enhance his growing reputation.
The deal is expected to be concluded in time to allow the teenager to figure in the Boxing Day encounter with Tony Adams's Wycombe Wanderers.
