A professional competitor since 2014, he was the former Thunderstrike Fight League Light heavyweight champion in Poland.

Oleksiejczuk has a younger brother named Cezary, who is also a professional mixed martial artist.

[5] In turn after the weigh-ins, Cuțelaba was pulled from the event by USADA due to a potential Anti-Doping Policy violation stemming from its investigation into voluntary disclosures by Cuțelaba during an out-of-competition sample collections on October 18 and October 19.

[8] Oleksiejczuk returned to octagon one year later to face Gian Villante on February 23, 2019, at UFC Fight Night: Błachowicz vs.

[11] Oleksiejczuk faced Gadzhimurad Antigulov on April 20, 2019, replacing Roman Dolidze, at UFC Fight Night: Overeem vs.

[15] Oleksiejczuk faced Jimmy Crute on February 23, 2020, at UFC Fight Night 168.

[25] Oleksiejczuk was scheduled to face Albert Duraev, replacing injured Bruno Silva, on December 17, 2022, at UFC Fight Night 216.

[26] In turn, Duraev was forced to withdraw for undisclosed reasons and was replaced by Cody Brundage.

He won by first-round ground and pound technical knockout,[32] which earned him a Performance of the Night award.