On 11 July 2015 Wallisch won the vacant WBO European Heavyweight Title with a knockout win over Italian Fabio Tuiach early in the 2nd round.
He defended the title against Croatian Ivica Bacurin at the Maritim Hotel in Berlin, Germany, on 9 January 2016, winning the fight by unanimous decision after 12 rounds.
After three more wins (over Andre Bunga, Samir Barakovic, Bernard Adie) he faced Christian Hammer as undefeated, with a record of 19–0.
Their fight was the main event of a multi-fight card, and took place at the Dynamo Volleyball Arena in Moscow, Russia.
Gassiev floored Wallisch two times in the fourth round, and then attacked him with a stream of punches, and the referee stopped the fight right before the bell.