Müller's career never recovered, winning only two of his last nine fights (over Hans Schoenrath and Gustave Limousin), suffering knockouts at the hands of von Porat and Jack Petersen (in front of 50,000 spectators at Ninian Park), and failing in three attempts to take the BDB German heavyweight title from Vincenz Hower. In April 1934, Müller announced his decision to retire from boxing and return to his former profession as a baker. He did, however, return for one more fight, an eighth-round stoppage loss to Erwin Klein in November 1934. He retired with a record of 32 wins from 47 fights. After retiring from boxing, Müller took up professional wrestling, competing in the UK in the late 1930s. During World War II, Müller was initially exempted from military service due to an eye condition, but in March 1945 he was enrolled into the Volkssturm. He was shot dead by Allied forces during fighting for Berlin on 29 April 1945.