The announcement of her injury was made Tuesday at the Reagan Presidential Library in Simi Valley, where Regan was scheduled to attend a speech by House Budget Committee Chairman Paul Ryan of Wisconsin.
Library executive director John Heubusch said Reagan could not attend the event because of her injury and that she was watching it on TV from home.
A spokesperson said the accident took place six weeks ago. The recovery process is slow and for the time being, Reagan is not allowed to attend large events.
The former first lady is 90-years-old.
The Associated Press contributed to this report.