Based on their ranking, the tennis player was seeded third in the championship.

seeded 是动词 seed 的过去分词形式。seed 本意是"种子"，在体育比赛中引申为"确定种子选手"的意思，即根据选手实力预先排定比赛位置。 seeded third 表示"被列为第三号种子选手"，这种排名方式可以避免强手过早相遇。