Nylander was promoted from AHL Rochester on Monday before Buffalo's home game against the Toronto Maple Leafs, whose lineup features William Nylander.
Alexander Nylander was selected with the eighth pick in last year's draft and has nine goals and 18 assists in 62 games with Rochester. The forward also had five goals and seven assists representing Sweden at the world junior championships to finish tied with a tournament-leading 12 points.
William Nylander was the NHL's rookie of the month for March after scoring four goals and 10 assists in 14 games.