Jonáš Forejtek (born 10 March 2001) is a professional tennis player from the Czech Republic.

Forejtek has reached five career singles finals, with a record of 2 wins and 3 losses all on the ITF Futures Tour.

At the 2019 Australian Forejtek and compatriot partner Dalibor Svrčina won the boys' doubles title beating Americans Emilio Nava and Cannon Kingsley 7–6(7–5), 6–4 in the finals.

At the 2019 US Open, he defeated Emilio Nava 6–7(4–7), 6–0, 6–2 in the final to win the boys’ singles championship.

Forejtek made his ATP debut at 2020 Sofia Open receiving a wildcard entry into the singles main draw.