Taken with the 16th pick of the 2013 NHL Draft, the 6-foot-5, 220-pounder has one goal and a team-best plus-4 rating in three preseason games.
"Watching Nikita throughout training camp and the preseason has solidified our opinion that he will be a good, young hockey player for our organization going forward," Sabres general manger Darcy Regier said. "He has exceptional presence on the ice and we look forward to seeing him continue to develop as a player."
Zadorov had 25 points and 54 penalty minutes in 63 games with the London Knights of the Ontario Hockey League last season, and two goals and six points in 20 games to help London win the OHL title. In five games at the Memorial Cup, he had a pair of goals.