The Bengals have the option of picking up the 5th year clause in Greens contract that would pay him an average of the top 25 players at his position. That would essentially lock him up through the 2016 season if they chose to use the franchise tag after that.
In the past the Bengals have taken this approach with some of their higher profile free agents. The thought being that they won't be forced into a situation to overpay for a player early in his career.
The other side of this is in the two years (option year and franchise year) the guaranteed money would be large and you risk turning the player against the organization by forcing his hand. The Bengals do not want to get into another situation where one of the top players is frustrated with the team.
Many consider Calvin Johnson the top receiver in the league with someone like Larry Fitzgerald close behind. Their respective salaries are 150.5 million and 128.5 million. Both have over 50 million in guaranteed money. I think A.J. would use these benchmarks as a guide as any restructuring happens on his deal. He would probably get more than Fitzgerald and not as much as Johnson.
It will be interesting to see what happens with his option in the near future.