2021 Banja Luka Challenger – Singles

Tallon Griekspoor was the defending champion but chose not to defend his title.

Juan Manuel Cerúndolo won the title after defeating Nikola Milojević 6–3, 6–1 in the final.

Seeds
• # 🇸🇰 Andrej Martin (semifinals)

• # 🇦🇷 Juan Manuel Cerúndolo (champion)

• # 🇦🇷 Tomás Martín Etcheverry (semifinals)

• # 🇷🇸 Nikola Milojević (final)

• # 🇮🇳 Sumit Nagal (second round)

• # 🇷🇸 Danilo Petrović (first round)

• # 🇨🇿 Zdeněk Kolář (quarterfinals)

• # 🇨🇿 Vít Kopřiva (first round)