Jets fans will recall that Nick Mangold missed two games in 2011 with a high ankle sprain, but probably came back before he was 100% and seemed to be limited (although, to his credit, he played well). If Freeman's injury is of similar severity, then there would be a small possibility of him returning before the end of preseason. However, Mangold had walked off the field on his own power, so Freeman's injury may be more serious. A serious high ankle sprain can sideline a player for up to six months.
Depending on the expected timescale of his recovery, the Jets may be able to put Freeman on injured reserve with a "designated for return" designation. This would enable him to return to practice in week seven and re-join the active roster in week nine at the earliest. However, if any other players suffer injuries between now and the end of preseason, they may instead choose to save that designation for someone else.