Stadium: Court 1 Round: 25 Ground: Clay
| ITF M15 Heraklion | 2021/05/31 06:30 | Christian Sigsgaard v Sean Hodkin | 2-6,7-5,6-10 |
| ITF M15 Heraklion | 2021/05/30 09:00 | Matic Dimic v Christian Sigsgaard | 3-6,2-6 |
| ITF M15 Tbilisi | 2021/05/22 06:00 | Christian Sigsgaard v Alexander Shevchenko | 6-7,6-7 |
| ITF M15 Tbilisi | 2021/05/21 06:00 | Christian Sigsgaard v Benjamin Lock | 7-5,6-1 |
| ITF M15 Tbilisi | 2021/05/20 06:00 | Christian Sigsgaard v Yurii Dzhavakian | 6-2,6-4 |
| ITF M15 Tbilisi | 2021/05/19 07:25 | Sanjar Fayziev v Christian Sigsgaard | 4-6,3-6 |
| ITF M15 Tbilisi | 2021/05/17 06:00 | Piotr Grynkowski v Christian Sigsgaard | 3-6,3-6 |
| ITF M15 Tbilisi | 2021/05/17 05:30 | Charles Minc v Christian Sigsgaard | 4-6,3-6 |
| Challenger Amersfoort | 2021/07/13 10:15 | Ryan Nijboer v Johan Nikles | 6-7,2-6 |
| 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 |