The 2021 European Open was a men's tennis tournament played on indoor hard courts. It was the sixth edition of the European Open and part of the ATP Tour 250 series of the 2021 ATP Tour. It took place at the Lotto Arena in Antwerp, Belgium, from 18 October until 24 October 2021.
The following players received wildcards into the singles main draw:
The following players received entry from the qualifying draw:
The following pairs received wildcards into the doubles main draw: