After his return to the Celtic team, Wieghorst became a mainstay in the Danish national team from October 1997. He was selected to represent Denmark at the 1998 FIFA World Cup, and played three games at the tournament. Most remarkably, he came on as a substitute in the 82nd minute of the 1–1 draw with South Africa, only to be sent off three minutes later. In Denmark's ultimate qualification game for the 2000 European Championship, he scored in the 3–2 victory against Italy which secured Denmark's qualification for the main tournament. Having been brought on as a substitute in the 52nd minute, he scored to level the game at 2–2 in the 57th minute, before he was sent-off for his second yellow card in the 80th minute. This made him the only Danish national team player to have been sent-off more than once. In October 1999, Wieghorst's national team career came to a halt again, due to his illness.