| UTR Pro Tennis Series Amsterdam | 2021/11/01 13:30 | Miko Wassermann v Guy Den Heijer | 2-6,5-7 |
| ITF M15 Girona | 2021/10/19 08:00 | Guy Den Heijer v Vladislav Ivanov | 6-4,6-3 |
| ITF M15 Girona | 2021/10/18 08:00 | Guy Den Heijer v Samir Hamza Reguig | 6-2,6-1 |
| ITF M15 Girona | 2021/10/17 08:00 | Guy Den Heijer v Ervin H Eminefendic | 6-3,6-1 |
| ITF M15 Platja D'Aro | 2021/10/14 14:15 | Jose Fco. Vidal Azorin v Guy Den Heijer | 7-6,1-6,6-2 |
| ITF M15 Platja D'Aro | 2021/10/13 12:00 | Guy Den Heijer v Fermin Tenti | 6-4,3-6,6-1 |
| ITF M15 Platja D'Aro | 2021/10/12 08:30 | Guy Den Heijer v Marc Othman Ktiri | 6-4,6-2 |
| ITF M15 Platja D'Aro | 2021/10/11 08:30 | Guy Den Heijer v Aaron Cohen | 4-6,7-6,10-4 |
| ITF M25 Hamburg | 2021/10/17 07:55 | Romain Faucon v Jip Van Assendelft | 1-6,6-1,11-9 |
| ITF M25 Sintra | 2021/09/15 15:20 | Jip Van Assendelft v Rio Noguchi | 6-4,0-6,1-6 |
| ITF M25 Sintra | 2021/09/14 09:55 | Jip Van Assendelft v Mirko Lagasio | 7-6,6-0 |
| ITF M25 Sintra | 2021/09/13 16:30 | Henrik Heise Korsgaard v Jip Van Assendelft | 6-3,4-6,5-10 |
| ITF M25 Eupen | 2021/09/07 07:30 | Juan Ignacio Galarza v Jip Van Assendelft | 4-6,6-2,10-3 |
| ITF M25 Eupen | 2021/09/06 09:15 | Jip Van Assendelft v Jing L Weng | 6-4,6-1 |
| ITF M25 Eupen | 2021/09/05 12:00 | Jip Van Assendelft v Joris Hoogland | 6-2,6-1 |
| ITF M25 Alkmaar | 2021/06/20 12:00 | Jip Van Assendelft v Benjamin Dhoe | 2-6,3-6 |