The NHL has blocked the Buffalo Sabres' bid to send rookie centre Mikhail Grigorenko to the minors on a conditioning assignment.

The Sabres announced the decision Wednesday, a day after Grigorenko was among three rookies assigned to AHL Rochester. Under league rules, teams are allowed to assign players on conditioning stints lasting no more than 14 days.

The ruling limits Buffalo's options. The Sabres must choose between keeping the 19-year-old in Buffalo or returning Grigorenko to his Canadian junior team in Quebec.

"We determined that the assignment would not have been consistent with our obligations under the league's agreement with the CHL," said NHL spokesman Frank Brown.

Grigorenko had difficulty earning playing time in Buffalo. Before the demotion, he missed two straight games and five of seven as a healthy scratch.

The Sabres also recalled centre Luke Adam and defenceman Brayden McNabb from Rochester.