1991 Swiss Indoors – Singles

John McEnroe was the defending champion, but lost in the final to Jakob Hlasek. The score was 7–6(7–4), 6–0, 6–3.

Seeds
• # 🇩🇪 Michael Stich (first round)

• # Karel Nováček (quarterfinals)

• # 🇪🇸 Sergi Bruguera (second round)

• # Petr Korda (second round)

• # 🇷🇺 Andrei Cherkasov (first round)

• # Jakob Hlasek (champion)

• # Alexander Volkov (semifinals)

• # 🇺🇸 John McEnroe (final)