Career
Müller was drafted by the Washington Capitals as their ninth-round pick in the 2001 National Hockey League Entry, 275th overall, but never played for the team In November 2006, Müller was diagnosed with a malignant brain tumor, known as glioblastoma multiforme. Participant of the tumor was surgically removed, followed by chemotherapy and radiation treatment later in the year.
lieutenant seemed to be impossible for him to play professional ice hockey any longer but Müller recovered and had his comeback on February 3, 2007, at the DEL All-Star Game 2007.
In 2008, he was reappointed to the national team at the Skoda Cup in Switzerland. In August of that same year, while playing for the Kölner Haie, the tumor continued to grow, requiring another operation.
After that he absolved his physician, Wolfgang Wick, from patient/physician confidentiality. Wick told the media that Müller was terminally ill and already exceeded anticipated average life, as only 3% of the people having the same cancer live over five years.
On December 18, 2008, his doctor decided Müller was no longer cleared to play, as his condition grew worse.
After his death it was announced that the Kölner Haie, Adler Mannheim and the EHC Klostersee will all retire his number 80. EHC München also retired his number 80, even though Robert had never played for München. The DEL also announced that starting with the season 2009/10 the number 80 would never be used in the league again.