The Jets placed Onwuasor (knee) on injured reserve Monday, Ethan Greenberg of the team's official site reports.
Onwuasor was poised to log a major workload at inside linebacker with the Jets this year, but he's expected to miss at least the first month of the season with a knee injury. He'll be required to sit out the first three weeks at a minimum. For the time being, Neville Hewitt and Blake Cashman are expected to start while Avery Williamson rotates in.