Katja Schlegel/Sebastian Keiser (Zug, SUI) qualified for the 2021 Oberstdorf International Mixed Doubles Cup playoffs, dropping their quarterfinals match 10-8 against Adela Walczak/Andrzej Augustyniak (Lodz, POL). of the 2021 Oberstdorf International Mixed Doubles Cup in Oberstdorf, Germany;
 
Schlegel/Keiser finished 3-1 in the 16-team qualifying round. . In their opening game, Schlegel/Keiser defeated Marie Kaldvee/Harri Lill (Tallinn, EST) 9-7, then went on to lose 12-4 against Pia-Lisa Schoell/Klaudius Harsch (Fuessen, GER). Schlegel/Keiser responded with a 7-6 win over Martine Ronning/Mathias Braenden (Lillehammer, NOR). Schlegel/Keiser won 9-4 against Lea Hueppi/Jonas Weiss (Kusnacht, SUI) in their final qualifying round match.
 
. For week 6 of the event schedule, Schlegel/Keiser did not improve upon their best events, remaining at 778th place on the World Ranking Standings with 6.288 total points. Schlegel/Keiser ranks 461st overall on the Year-to-Date rankings with 0.000 points earned so far this season.