Jan Hájek is a male professional tennis player from the Czech Republic. He is right-handed with a double handed backhand. He reached his highest singles ATP-ranking on November 6, 2006, when he reached world number 71.
Hájek turned professional in 2000 and won his first Futures event in Negril of the same year defeating Johan Ortegren in the final. Between 2000 and 2003 Hájek played primarily on the Futures circuit, then after that he played some Challenger events as well as the Futures tournaments. At the end of 2005 he had won 8 Futures titles all on clay, which is his best surface.
2006 was the breakthrough season for Hájek, as he started the year ranked at 352 and then finished the season ranked at 76th in the world. Hájek won his first challenger in Barletta as a qualifier easily defeating Stefano Galvani 6-2 6-1 in the final. In May Hájek qualified for the challenger in Prague before losing to compatriot Robin Vik in the final. Hájek won three more Challengers during the year including two major ones in Prostějov where he got a retirement victory over Tomáš Berdych and Braunschweig defeated Fernando Vicente in straight sets. He won the Poznań Challenger without losing a set. In addition to the three Challenger titles, Hájek made his debut at Grand Slam level where he defeated Lukáš Dlouhý in straight sets before losing to Fernando González.