Bristol City keeper Dean Gerken has been sidelined with a groin injury, picked up in his side's 1-0 friendly defeat at Bath City.
Robins boss Keith Millen told the club's website: "We're assessing weekly with him and the medical staff."
Millen said that he could enter the transfer market if Gerken, 25, is not fit to challenge first-choice keeper David James at the start of the season.
"We would consider bringing in another keeper on a temporary basis," he added.
In the meantime, first-year professional Lewis Carey will deputise against Forest Green Rovers.