  Knockout tournaments constitute a popular format for organizing sports
competitions. While prior results have shown that it is often possible to
manipulate a knockout tournament by fixing the bracket, these results ignore
the prevalent aspect of player seeds, which can significantly constrain the
chosen bracket. We show that certain structural conditions that guarantee that
a player can win a knockout tournament without seeds are no longer sufficient
in light of seed constraints. On the other hand, we prove that when the
pairwise match outcomes are generated randomly, all players are still likely to
be knockout winners under the same probability threshold with seeds as without
seeds. In addition, we investigate the complexity of deciding whether a
manipulation is possible when seeds are present.
