Pope, 21, has been drafted in as cover for Michael Ingham, sidelined due to a groin injury, and is expected to go straight into the starting line-up for Saturday's league game at Southend.
Fellow new signing Keith Lowe, 28, will also be in contention for the weekend. Both players have joined for an initial month.
Pope's only appearance for Charlton to date came as a substitute on the final day of last season against Bristol City, while he has had loan spells at Cambridge and Aldershot.
Meanwhile, York defender Tom Allan has joined Harrogate Town on loan for a month. Team-mate Tom Platt spent a similar period on loan at the Skrill North side last season.