Stadium: KNLTB Court Round: 25 Ground: Clay
| ITF M25 Marburg | 2021/07/10 11:00 | Ryan Nijboer v Nick Hardt | 2-6,4-6 |
| ITF M25 Marburg | 2021/07/09 12:00 | Ryan Nijboer v Milan Welte | 4-6,6-3,6-1 |
| ITF M25 Marburg | 2021/07/08 09:00 | Ryan Nijboer v Tim Handel | 6-3,6-4 |
| ITF M25 Marburg | 2021/07/07 09:00 | Yan Sabanin v Ryan Nijboer | 0-6,3-6 |
| ITF M25 The Hague | 2021/06/30 12:55 | Mateus Alves v Ryan Nijboer | 7-6,6-3 |
| ITF M25 Alkmaar | 2021/06/24 12:00 | Marko Tepavac v Ryan Nijboer | 4-6,7-6,6-1 |
| ITF M15 Skopje | 2021/06/10 11:30 | Miljan Zekic v Ryan Nijboer | 6-2,6-3 |
| ITF M15 Skopje | 2021/06/10 07:45 | Ryan Nijboer v Dian Nedev | 6-3,6-2 |
| Challenger Amersfoort | 2021/07/12 09:00 | Jeremy Jahn v Johan Nikles | 2-6,3-6 |
| Challenger Amersfoort | 2021/07/11 14:00 | Dominik Palan v Johan Nikles | 4-6,6-7 |
| ITF M25 The Hague | 2021/07/03 08:00 | Javier Barranco Cosano v Johan Nikles | 7-5,6-4 |
| ITF M25 The Hague | 2021/07/02 10:30 | Mateus Alves v Johan Nikles | 2-6,6-7 |
| ITF M25 The Hague | 2021/07/01 10:50 | Johan Nikles v Julian Ocleppo | 6-4,6-1 |
| ITF M25 Klosters | 2021/06/23 09:25 | Johan Nikles v Mohamed Aziz Dougaz | 2-6,7-6,3-6 |
| ITF M15 Genova | 2021/06/20 08:00 | Johan Nikles v Luca Nardi | 4-6,2-6 |
| ITF M15 Genova | 2021/06/19 15:00 | Edoardo Eremin v Johan Nikles | 2-6,3-6 |