[3] In 1931, Knottenbelt reached the second round of the men's singles at Wimbledon, losing to Eberhard Nourney of Germany, 8–10 6–2, 0–6 9–11.
[4] In the 1932 Wimbledon mixed doubles, he and Madzy Rollin Couquerque lost in the fourth round to Ellsworth Vines and Helen Wills-Moody.
[5][6] In the quarterfinals of the 1934 Davis Cup, he lost to Swedes Curt Östberg (1–6, 1–6, 4–6) and Kalle Schröder (1–6, 5–7, 0–6) although the Netherlands won the round.
[7] Knottenbelt was born in the Dutch East Indies but grew up in Bussum.
His younger brother Anthony Knottenbelt was also a promising tennis player, but died at the age of 19 after an accident.