Allen sustained an MCL sprain during Monday's 27-21 loss at Miami and likely will be placed on injured reserve, Ian Rapoport of NFL Network reports.
Prior to injuring his knee on a kick return in the second quarter, Allen was splitting the reps at running back with Breece Hall, with the former turning his four carries into 26 yards. If Allen requires a stint on IR, he'll be required to miss at least four games. In the meantime, Hall likely will take on a workhorse role out of the Jets backfield, while Isaiah Davis would be the top candidate to handle any reps that don't go to Hall.