Pekar did not participate in training camp due to an injury and was placed on the team's non-roster injured reserve at the start of the season.
He will join a Rochester club that split its first two games last weekend against the Toronto Marlies. The Amerks will next play on Wednesday against Belleville.
Selected by the Sabres in the fourth round of the 2018 NHL Draft, Pekar recorded six points (3+3) in 47 AHL games last season.