Arnaudov was born in Bulgaria in 1992. Son of Bulgarian emigrants in Portugal since the age of 12, he acquired Portuguese citizenship on 2 July 2010 (aged 18). Since then he represented Portugal at the 2011 European Junior Championships and the 2013 European U23 Championships in shot put, but was eliminated in the qualifying round both times. In 2014 he broke the Portuguese under-23 record with a throw of 18.80 m.