Štajner started his active footballing career in the youth teams of SK Dynamo České Budějovice.

He failed to make a breakthrough at Slavia, continuing his youth career with TJ Senohraby, an amateur club close to the city where he grew up - Benešov.

In 1998, Štajner moved on to MUS Most in an attempt to advance his career, although his breakthrough was to come at the beginning of the new millennium after signing for Slovan Liberec, as he became known as an excellent goalscorer and attracted attention with his European performances in the UEFA Cup.

On 22 May 2003, Štajner helped cement his status as a cult hero for the club, notably scoring the decisive goal against Borussia Mönchengladbach to retain Hannover's place in the top flight.

[4] Štajner was a member of the Czech Republic national team, and played in the 2006 FIFA World Cup.