2021 European Open
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.
Finals
Singles
- Jannik Sinner defeated Diego Schwartzman, 6–2, 6–2
Doubles
- Nicolas Mahut / Fabrice Martin defeated Wesley Koolhof / Jean-Julien Rojer, 6–0, 6–1
Singles main-draw entrants
Seeds
- Rankings are as of 4 October 2021.
Other entrants
The following players received entry from the qualifying draw:
;Before the tournament
- Félix Auger-Aliassime → replaced by Alexei Popyrin
- Nikoloz Basilashvili → replaced by Gianluca Mager
- Pablo Carreño Busta → replaced by Jordan Thompson
- Grigor Dimitrov → replaced by Arthur Rinderknech
- Fabio Fognini → replaced by Lorenzo Musetti
- Ugo Humbert → replaced by Jan-Lennard Struff
- Cameron Norrie → replaced by Botic van de Zandschulp
Doubles main-draw entrants
Seeds
- Rankings are as of 4 October 2021.
Other entrants
- Ruben Bemelmans / Kimmer Coppejans
- Lloyd Harris / Xavier Malisse
Withdrawals
- Simone Bolelli / Máximo González → replaced by David Pel / Botic van de Zandschulp
- Grigor Dimitrov / Frederik Nielsen → replaced by Frederik Nielsen / Matej Sabanov
- Fabio Fognini / Roman Jebavý → replaced by Roman Jebavý / Andrei Vasilevski
- Cristian Garín / David Vega Hernández → replaced by Federico Delbonis / David Vega Hernández
- Nikola Mektić / Mate Pavić → replaced by Jonathan Erlich / André Göransson
- John Peers / Filip Polášek → replaced by Romain Arneodo / Matt Reid
- Tim Pütz / Michael Venus → replaced by Denys Molchanov / Aleksandr Nedovyesov
- Lorenzo Musetti / Benoît Paire