McFadden, a third-round pick of the Browns in 2013, played every game last season and started the final two preseason games due to injuries in the Browns' secondary.
The Jets had to do something after a tumultuous preseason.
Top corner Dee Milliner suffered a high-ankle sprain on Aug. 10, and is highly questionable for the season opener against the Oakland Raiders. The other projected starter, Dimitri Patterson, was suspended and released Saturday after an unexcused absence last weekend. They also lost rookie Dexter McDougle to a season-ending knee injury in early August.
It means the Jets' starting corners in Week 1 will be Darrin Walls, a career backup, and converted safety Antonio Allen -- assuming Allen is cleared after suffering a concussion in the third preseason game.
Right now, their most experienced, healthy corner is Kyle Wilson, who is used exclusively in the slot.
The situation is so dire that Rex Ryan had to pick up a castoff from his former protégé, Browns coach Mike Pettine.
The upside is that McFadden already is familiar with the system, as Pettine and Ryan employ similar schemes. The concern, from a Jets perspective, is that McFadden failed to stick in Cleveland despite a rash of cornerback injuries.
McFadden, out of San Diego State, recorded 16 tackles, one pass breakup and no interceptions in 233 defensive snaps (22 percent) last season. He started the final two preseason games in place of Joe Haden. McFadden struggled against the Chicago Bears in the finale, committing a 37-yard pass interference penalty and surrendering a 32-yard completion.
To make room for McFadden, the Jets waived cornerback LeQuan Lewis.
Meanwhile, they signed quarterback Matt Simms to the practice squad, according to a source. Simms was released Saturday and cleared waivers.