Tomas Nydahl ( born March 21, 1968 in Linköping ) is a former Swedish tennis player.
Nydahl began at the age of seven years with the tennis game. In the junior competition he was in the final of the Swedish Indoor Junior Championships and the semifinals of the Italian Open Juniors. In 1987 he was a professional tennis player and reached the following year at the Challenger tournaments of Bossonnens and Strasbourg respectively the final. In 1989 he was in Bologna on the side of his compatriot Jörgen Windahl first time in the final of the ATP tournament, but they lost to the Spaniards Sergio Casal and Javier Sánchez clearly in two sentences. In the following years he focused on the Challenger tour, 1990, he won with Peter Nyborg in Munich his first doubles title on the Challenger tour, another doubles title followed in the next year in Bucharest.
In 1993, he won his first singles title in Emden on the Challenger Tour and stood at the Swedish Open in the doubles final. In the following years he won several more singles and doubles titles and the Challenger Tour. In 1997, he reached for the last time an ATP doubles final, a title on the ATP World Tour, he could never win. Its highest listing in the tennis world ranking he reached in 1998 with position 72 in singles and in 1989 with position 103 in doubles.