Siemian suffered a lower leg injury in Monday's game against the Browns and has been replaced by Luke Falk, Rich Cimini of ESPN.com reports.
The injury appears to be significant, as Siemian got his leg caught underneath him while receiving a late hit from Browns defensive end Myles Garrett in the second quarter. He did not have much success through the air filling in for regular starter Sam Darnold (illness), taking two sacks and completing three of six passes for three yards. The Jets now turn to Luke Falk, who was signed off the practice squad hours before Monday's game.