The Jets missed the playoffs in that campaign and struggled to a 6-10 record in the 2012 season after reaching back-to-back AFC Championship games in the two years prior.
Ryan told the New York Post: "It started with the Giants game. When we lost the Giants game, that really killed us. I think our team was so focused on playing Giants.
"Eli [Manning] was 9-of-27 in that game. Go back and look. That kind of snowballed us. They used it to accelerate and we went like this (pointing down)."
The Jets begin their 2013 season at Cleveland Browns on September 8.