# 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)

## Draw
### Key

* Q = Qualifier
* WC = Wild card
* LL = Lucky loser
* Alt = Alternate
* SE = Special exempt
* PR = Protected ranking
* ITF = ITF entry
* JE = Junior exempt
* w/o = Walkover
* r = Retired
* d = Defaulted
* SR = Special ranking

### Finals

| Semifinals | Semifinals | Semifinals | Semifinals | Final | Final | Final | Final |
| 1 | Andrej Martin | 2 | 4 | | | | |
| 4 | Nikola Milojević | 6 | 6 | | | | |
| 4 | Nikola Milojević | 6 | 6 | 4 | Nikola Milojević | 3 | 1 |
| | | | | 2 | Juan Manuel Cerúndolo | 6 | 6 |
| 3 | Tomás Martín Etcheverry | 3 | 3 | 2 | Juan Manuel Cerúndolo | 6 | 6 |
| 2 | Juan Manuel Cerúndolo | 6 | 6 | | | | |

### Top half

| First round | First round | First round | First round | First round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 1 | A Martin | 0 | | | | | | | | | | | | | | |
| | M Guinard | 0$^r$ | | | 1 | A Martin | 6 | 7 | | | | | | | | |
| Q | J Mridha | 6 | 6 | | Q | J Mridha | 3 | 5 | | | | | | | | |
| | D Stricker | 2 | 3 | | | | | | 1 | A Martin | 7$^7$ | 6 | | | | |
| WC | Dražen Petrović | 1 | 0 | | | | | | | C Gómez-Herrera | 6$^2$ | 3 | | | | |
| | C Gómez-Herrera | 6 | 6 | | | C Gómez-Herrera | 7 | 6 | | | | | | | | |
| | N Álvarez | 1 | 2 | | 5 | S Nagal | 5 | 3 | | | | | | | | |
| 5 | S Nagal | 6 | 6 | | | | | | | | | | 1 | A Martin | 2 | 4 |
| 4 | N Milojević | 6 | 6 | | | | | | | | | | 4 | N Milojević | 6 | 6 |
| WC | Vladan Tadić | 0 | 3 | | 4 | N Milojević | 6 | 1 | | | | | | | | |
| | P Krstin | 6 | 3 | 6 | | P Krstin | 1 | 1$^r$ | | | | | | | | |
| | N Moreno de Alboran | 2 | 6 | 2 | | | | | 4 | N Milojević | 6 | 6 | | | | |
| | D Kuzmanov | 3 | 6 | 6 | | | | | 7 | Z Kolář | 3 | 0 | | | | |
| | A Shevchenko | 6 | 4 | 1 | | D Kuzmanov | 5 | 2 | | | | | | | | |
| | M Zekić | 3 | 1 | | 7 | Z Kolář | 7 | 6 | | | | | | | | |
| 7 | Z Kolář | 6 | 6 | | | | | | | | | | | | | |

### Bottom half

| First round | First round | First round | First round | First round | Second round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 6 | D Petrović | 6 | 6$^4$ | 2 | | | | | | | | | | | | | |
| WC | M Topo | 4 | 7$^7$ | 6 | WC | M Topo | 6 | 3 | 7$^7$ | | | | | | | | |
| | N Fatić | 7 | 4 | 1 | | V Sachko | 1 | 6 | 6$^5$ | | | | | | | | |
| | V Sachko | 5 | 6 | 6 | | | | | | WC | M Topo | 3 | 6$^6$ | | | | |
| Q | M Cuevas | 2 | 4 | | | | | | | 3 | TM Etcheverry | 6 | 7$^8$ | | | | |
| | N Serdarušić | 6 | 6 | | | N Serdarušić | 6 | 6$^4$ | 1 | | | | | | | | |
| Q | David Poljak | 2 | 5 | | 3 | TM Etcheverry | 4 | 7$^7$ | 6 | | | | | | | | |
| 3 | TM Etcheverry | 6 | 7 | | | | | | | | | | | 3 | TM Etcheverry | 3 | 3 |
| 8 | V Kopřiva | 3 | 6 | 6$^5$ | | | | | | | | | | 2 | JM Cerúndolo | 6 | 6 |
| | M Bašić | 6 | 4 | 7$^7$ | | M Bašić | 2 | 4 | | | | | | | | | |
| | C-h Tseng | 6 | 6 | | | C-h Tseng | 6 | 6 | | | | | | | | | |
| | A Vatutin | 1 | 4 | | | | | | | | C-h Tseng | 2 | 0 | | | | |
| | M Pecotić | 4 | 6 | 7$^7$ | | | | | | 2 | JM Cerúndolo | 6 | 6 | | | | |
| Q | M Tepavac | 6 | 3 | 6$^0$ | | M Pecotić | | | | | | | | | | | |
| | M Jaziri | 6 | 3 | 4 | 2 | JM Cerúndolo | w/o | | | | | | | | | | |
| 2 | JM Cerúndolo | 1 | 6 | 6 | | | | | | | | | | | | | |