The 21-year-old has not featured for the Robins since October after going out on loan to Bath City, but will undergo surgery this week in an attempt to make a return to first-team action.
Hooman is manager Mark Yates' only injury concern at the moment, with an otherwise fully-fit squad to choose from ahead of Friday's trip to Morecambe.
Senior sports therapist Ian Weston told the club's official website: "It's a blow for Harry.
"He will go into surgery and will be in a cast for two weeks following the operation.
"He'll then be moved into another cast for another four weeks which will give him more movement in the foot but, after that, it will be a period of rehab to get back fit and involved."