 On 2 October 2019, Ondrášek received his first senior call up from the Czech Republic for their UEFA Euro 2020 qualifier against England.On 11 October in his international debut, he came on as a substitute and scored the winning goal for the Czech Republic in their 2–1 victory over England.Nicknamed "The Cobra" () due to a large tattoo of a cobra on his back, Ondrášek sports a host of other tattoos.