The Lions could have automatically extended the 26-year-old's deal into a fifth year to keep him under contract through the 2015 season, but due to his inconsistent play Mayhew believes that he wouldn't be worth the price tag.
He told the club's official website: "He's a phenomenal talent. This guy can be whatever he wants to be. That's probably why I'm on him so hard.
"It's an opportunity for him to go out and perform his best this off-season, perform his best during the season and hopefully it helps him become the best player he can possibly be.
"[The option] is $5.5 million and I have to ask myself, 'Is he a $5.5 million player?' There's some performances where he is. There's some performances where he's not."
Fairley recorded 36 tackles and six sacks for the Lions in the 2013 season.