[2] Krsek made his international debut at the 2015 European Youth Olympic Festival in Tbilisi, Georgia.

The following year, he would return to Tbilisi for the 2016 European U18 Championships where he finished in seventh place in the 200 metres again.

He was an unused member of the Czech relay team at the delayed 2020 Olympic Games in Tokyo in 2021.

[5] He was part of the Czech team that won the bronze medal in the 4 × 400 metres mixed relay at the 2023 World Athletics Championships in Budapest in a new national record time of 3:11.98.

[6] Selected for the 2024 World Athletics Indoor Championships in Glasgow, he reached the final of the men's 400 meters where he finished in sixth place.