Source: Mike Halford, NBC Sports Pro Hockey Talk 
Mikhail Grigorenko won’t be going to the Rochester Americans after all.
On Wednesday, the Sabres announced their plan to send Grigorenko to the AHL on a conditioning assignment was ruled against by the NHL:
Mikhail Grigorenko has also been returned to #Sabres  after conditioning assignment ruled against by NHL.
— Sabres PR (@SabresPR) November 20, 2013 
NHL Turns Down Grigorenko's AHL Assignment by Sports Talk Florida
(2/2)…the Sabres’ assignment for Grigorenko was ruled against by the NHL and the team respects the League’s decision.
— Sabres PR (@SabresPR) November 20, 2013