2021 Hamburg European Open – Men's singles

Andrey Rublev was the defending champion, but chose to not defend his title as he and other Russian Olympic athletes were sent to Yuzhno-Sakhalinsk for training sessions.

Pablo Carreño Busta won his maiden ATP Tour 500 singles title, defeating Filip Krajinović in the final, 6–2, 6–4.

Seeds
The top four seeds received a bye into the second round. • # Stefanos Tsitsipas (quarterfinals)

• #🇪🇸 Pablo Carreño Busta (champion)

• # Nikoloz Basilashvili (quarterfinals)

• #🇪🇸 Albert Ramos Viñolas (second round)

• #🇷🇸 Dušan Lajović (quarterfinals)

• #🇷🇸 Filip Krajinović (final)

• #🇩🇪 Jan-Lennard Struff (first round)

• #🇫🇷 Benoît Paire (quarterfinals)

Seeds
• # 🇪🇸 Carlos Taberner (qualified)

• # 🇧🇷 Thiago Seyboth Wild (qualified)

• # 🇸🇰 Jozef Kovalík (first round)

• # 🇧🇦 Damir Džumhur (first round)

• # 🇦🇺 Christopher O'Connell (qualifying competition)

• # 🇵🇪 Juan Pablo Varillas (qualified)

• # 🇮🇳 Sumit Nagal (qualifying competition; Lucky loser)

• # 🇩🇪 Oscar Otte (first round)

• # 🇸🇰 Alex Molčan (qualified)

• # 🇦🇷 Sebastián Báez (qualifying competition; Lucky loser)

• # 🇮🇹 Alessandro Giannessi (qualifying competition)

• # 🇷🇸 Danilo Petrović (first round)

Qualifiers
• # 🇪🇸 Carlos Taberner

• # 🇧🇷 Thiago Seyboth Wild

• # 🇨🇳 Zhang Zhizhen

• # 🇩🇪 Maximilian Marterer

• # 🇸🇰 Alex Molčan

• # 🇵🇪 Juan Pablo Varillas

Lucky losers
• # 🇮🇳 Sumit Nagal

• # 🇦🇷 Sebastián Báez