In his childhood Weißhaidinger competed in gymnastics, but dropped that sport after growing too tall and concentrated on athletics. Weißhaidinger won gold in both the shot (20.35 m/5 kg) and the discus (60.94 m/1.5 kg) at the 2009 European Youth Olympic Festival in Tampere. He also competed in both events at the 2009 World Youth Championships and the 2010 World Junior Championships; in the shot he placed fourth in 2009 and sixth in 2010, while in the discus he went out in qualifying both times.