The club borrowed £1.5 million from its football board chairman Sandy Easdale and shareholder George Letham earlier this year on the understanding that the money would be paid back when cash was secured from season ticket sales.
However, following an announcement that more than 17,000 tickets have been sold, the loans remain unpaid.
Rangers claim they have until September 1 to pay the money back under the terms of the agreement, but fans have voiced concern.
Chris Graham, spokesman for supporters group Union of Fans, said: "The deal's quite clear - it says it's to be paid out of the first £1.5 million to come in from the club season ticket sales."
A Rangers spokesman said: "The loan will be repaid in accordance with the terms of the agreement."