The apology was posted Wednesday afternoon, shortly after Spiller used the term while exchanging tweets with close friend and former Clemson teammate, Philadelphia Eagles defensive end Ricky Sapp. The original tweet has been deleted.
In apologizing, Spiller wrote he was "truly sorry," and that it was out of character, before closing with "God Bless."
ProFootballTalk.com first reported about Spiller's tweet on its website.
Bills spokesman Scott Berchtold says the team "will reserve comment" until it speaks with Spiller on Thursday.