Allen sustained a concussion during the Jets preseason game on Aug. 22 and had to go through the NFL's post-concussion assessment protocol.
A former seventh round pick, Allen recently converted from free safety to cornerback, a position of need for the team.
Head coach Rex Ryan said Tuesday that he isn't sure if cornerback Dee Milliner will be able to play in Week 1 as he continues to recover from a high ankle sprain. On Saturday, the Jets released CB Dimitri Patterson, and rookie CB Dexter McDougle tore his ACL and was lost for the season last month.
Allen, 25, made 60 tackles and grabbed one interception as a safety for New York in 2013.
- Molly Geary