The event takes place on June 20 at O2 World in Berlin, Germany.
Local boy Hein will be returning to the venue in which he made his debut for the UFC in 2014.
Sajewski, the Polish lightweight, will be looking to continue his run of form which sees him unbeaten in his professional career at 13-0-0.
Hein feels that the fan support he gets in Germany will play a huge part in how well he does on fight night.
"I can't wait to fight in Berlin again. I will never forget how the fans supported me last year; I still get goose bumps thinking of it.
"German fans are simply the best ! I just came back from my first training camp in Thailand and am already burning to step back into the octagon."
The other keenly anticipated fight's on the card will be between Niklas Backstrom and Noad Lahat alongside the main event, which has No.2 ranked light heavyweight, Alexander "The Mauler" Gustafsson up against No.6 ranked, Glover Teixeira, in a five round main event.