2021 ATP Lyon Open – Singles

Benoît Paire was the defending champion from when the event was last held in 2019, but chose to participate in Geneva instead.

Stefanos Tsitsipas won the title, defeating Cameron Norrie in the final 6–3, 6–3.

Seeds
The top four seeds received a bye into the second round. • # 🇦🇹 Dominic Thiem (second round)

• # Stefanos Tsitsipas (champion)

• # 🇦🇷 Diego Schwartzman (second round)

• # 🇧🇪 David Goffin (second round)

• # 🇫🇷 Gaël Monfils (second round)

• # 🇮🇹 Jannik Sinner (second round)

• # 🇨🇦 Félix Auger-Aliassime (first round)

• # 🇷🇺 Karen Khachanov (semifinals)

Seeds
• # 🇮🇹 Lorenzo Musetti (moved to the main draw)

• # 🇸🇪 Mikael Ymer (qualified)

• # João Sousa (qualified)

• # 🇫🇷 Grégoire Barrère (qualified)

• # 🇫🇷 Arthur Rinderknech (qualifying competition, lucky loser)

• # 🇧🇷 Thiago Seyboth Wild (qualifying competition, lucky loser)

• # 🇵🇱 Kamil Majchrzak (qualified)

• # 🇫🇷 Antoine Hoang (qualifying competition)

Qualifiers
• # 🇵🇱 Kamil Majchrzak

• # 🇸🇪 Mikael Ymer

• # João Sousa

• # 🇫🇷 Grégoire Barrère

Lucky losers
• # 🇫🇷 Arthur Rinderknech

• # 🇧🇷 Thiago Seyboth Wild