1991 Mercedes Cup – Singles

Goran Ivanišević was the defending champion, but lost in the second round to Andrés Gómez.

Michael Stich won the title by defeating Alberto Mancini 1–6, 7–6(11–9), 6–4, 6–2 in the final.

Seeds
All seeds received a bye to the second round. • # 🇩🇪 Michael Stich (champion)

• # 🇫🇷 Guy Forget (third round)

• # 🇪🇸 Emilio Sánchez (second round)

• # Goran Ivanišević (second round)

• # Andrei Cherkasov (second round)

• # Karel Nováček (second round)

• # Goran Prpić (quarterfinals)

• # 🇸🇪 Magnus Gustafsson (second round)

• # 🇦🇹 Horst Skoff (third round)

• # 🇸🇪 Jonas Svensson (second round)

• # 🇦🇷 Guillermo Pérez Roldán (third round)

• # Alexander Volkov (third round)

• # 🇮🇹 Omar Camporese (second round)

• # Ronald Agénor (third round)

• # 🇦🇷 Martín Jaite (second round)

• # 🇪🇸 Jordi Arrese (second round)