| Tennis de table - Rencontres | 12/09 18:50 | - | Nielsen, Claus v Andrej Gacina | L | 0-3 | |
| Qatar Open XD | 05/30 12:00 | 1 | Nielsen, Claus v Udra, Alfredas | - | Retired | |
| Qatar Open 2019, MS | 05/29 11:00 | 1 | Nielsen, Claus v Allahverdiyev, Vazir | W | 4-0 | |
| Qatar Open 2019, MS | 03/07 17:00 | - | Adam Szudi v Nielsen, Claus | L | 3-0 | |
| Qatar Open XD | 02/03 16:27 | - | Ismailov, Sadi v Nielsen, Claus | L | 4-2 | |
| Qatar Open XD | 02/02 13:19 | - | David Reitspies v Nielsen, Claus | W | 3-4 | |
| Qatar Open XD | 01/17 08:15 | - | Rares Sipos v Nielsen, Claus | L | 3-0 | |
| Qatar Open 2019, MS | 12/16 20:21 | - | Nielsen, Claus v Kuzmin, Fedor | W | 3-0 | |
| Qatar Open 2019, MS | 12/02 19:27 | - | Christophe Legout v Nielsen, Claus | L | 3-1 | |
| Qatar Open 2019, MS | 11/25 18:51 | - | Nielsen, Claus v Hugo Calderano | L | 0-3 | |
| Qatar Open 2019, MS | 11/25 16:37 | - | Nielsen, Claus v Yuto Muramatsu | L | 2-3 | |
| Qatar Open XD | 11/15 18:12 | - | Nielsen, Claus v O`Connor, M. | W | 3-0 | |
| Qatar Open XD | 11/10 19:46 | - | Nielsen, Claus v Enzo Angles | L | 0-3 | |
| Qatar Open XD | 11/10 10:27 | - | Devos, Robin v Nielsen, Claus | L | 4-2 | |
| Qatar Open XD | 11/09 12:01 | - | Nielsen, Claus v Kucera, Stanislav | L | 0-4 | |
| Qatar Open XD | 11/09 09:28 | - | Nielsen, Claus v Alessandro Baciocchi | W | 3-2 | |
| Qatar Open 2019, MS | 11/04 14:02 | - | Samsonov, Vladimir v Nielsen, Claus | L | 3-0 | |
| Qatar Open 2019, MS | 10/26 17:55 | - | Nielsen, Claus v Lundqvist, Jens | L | 2-3 | |
| Qatar Open 2019, MS | 10/07 16:54 | - | Hugo Calderano v Nielsen, Claus | L | 3-0 | |
| Qatar Open XD | 09/01 11:20 | - | Hampus Soderlund v Nielsen, Claus | L | 4-1 | |
| Bulgaria Open 2019, MS | 08/26 16:00 | 5 | Nielsen, Claus v Tran, Anthony | L | 2-4 | |
| Bulgaria Open 2019, MS | 08/26 12:55 | 6 | Karakasevic, Aleksandar v Nielsen, Claus | W | 3-4 |