The NHL blocked the Buffalo Sabres from sending rookie center Mikhail Grigorenko to Rochester of the American Hockey League on a conditioning assignment.
The 19-year Grigorenko was one of four rookies sent to the minors on Tuesday, but the Sabres announced the NHL's decision on Wednesday. According to league rules, a conditioning assignment can last no more than 14 days.
The ruling forces the Sabres to keep Grigorenko in Buffalo or return him to his Canadian junior team, the Quebec Remparts. But the Remparts already have the maximum two imports and would have to make a trade to clear room for Grigorenko.
"We determined that the assignment would not have been consistent with our obligations under the league's agreement with the CHL," NHL spokesman Frank Brown said.
The AHL-CHL agreement stipulates that CHL prospects must remain in major junior until they are age 20 or have played four full seasons. Grigorenko is not eligible to to play for Rochester full time.
Grigorenko has been a healthy scratch in five of the past seven games.
Also sent to Rochester on Tuesday were Rasmus Ristolainen and Johan Larsson. Nikita Zadorov was returned to London of the Ontario Hockey League.
In other roster moves, the Sabres recalled center Luke Adam and defenseman Brayden McNabb from Rochester.