A year of not being on the ice, or even just a few months of not being able to train, will destroy any player's conditioning. Martin Réway didn't perform to his top level in the Rookie Tournament or at Montreal Canadiens training camp, but that was to be expected. While he should be able to eventually get back in game shape, he still has multiple challenges ahead of him, one of which being the adjustment to a different style of play and a smaller rink.
Getting used to the AHL will take time. Fortunately, it's likely Sylvain Lefebvre will have an important place for him in the lineup when the season starts.