2021 Swiss Open Gstaad – Singles

Casper Ruud defeated Hugo Gaston in the final, 6–3, 6–2, to win the men's singles tennis title at the 2021 Swiss Open.

Albert Ramos Viñolas was the reigning champion from when the tournament was last held in 2019, but chose to compete in Umag instead.

Seeds
The top four seeds receive a bye into the second round. • # 🇨🇦 Denis Shapovalov (second round)

• # 🇪🇸 Roberto Bautista Agut (second round)

• # 🇳🇴 Casper Ruud (champion)

• # Cristian Garín (quarterfinals)

• # 🇦🇷 Federico Delbonis (second round)

• # 🇫🇷 Benoît Paire (quarterfinals)

• # 🇷🇸 Laslo Đere (semifinals)

• # 🇪🇸 Feliciano López (second round)

Seeds
• # 🇩🇪 Oscar Otte (qualified)

• # 🇵🇱 Kacper Żuk (qualifying competition, lucky loser)

• # 🇫🇷 Enzo Couacaud (qualifying competition, lucky loser)

• # 🇨🇦 Steven Diez (qualifying competition)

• # Ernests Gulbis (first round)

• # 🇩🇪 Maximilian Marterer (first round)

• # 🇦🇺 Aleksandar Vukic (first round)

• # 🇮🇹 Roberto Marcora (qualifying competition)

Qualifiers
• # 🇩🇪 Oscar Otte

• # Sandro Ehrat

• # 🇨🇿 Vít Kopřiva

• # 🇧🇪 Zizou Bergs

Lucky losers
• # 🇵🇱 Kacper Żuk

• # 🇫🇷 Enzo Couacaud