The Scottish Third Division leaders made the decision after a meeting with Sandaza and his agent on Friday morning.
Sandaza allegedly declared details of his salary and declared himself open to a move to a better league during a recorded hoax telephone conversation.
A club statement read: "Francisco Sandaza has been suspended by the club pending an investigation into comments made by the player in a recorded telephone conversation.
"The club, Francisco and his agent have had discussions and manager Ally McCoist also spoke with the player, who did not take part in today's training session.
"Francisco will not return to the club while the investigation is under way.
"Rangers regard this is an extremely serious issue but there will be no further comment until the inquiry, which could take a week, has been completed."