Italian tennis player Yannick Sinner and Pole Hubert Hurkacz withdrew from the ATP 500 tournament in Barcelona.
Botik van de Zandshulp and Tallon Grikspor will also not take part in the tournament.
They will be replaced by Maxim Cressy, Lorenzo Musetti, Jordan Thompspon and Roberto Carballes Baena. The organizers also removed one of the wild cards, and thus the American Brandon Nakashima will get a place at the base.
Earlier, Khurkach failed to qualify for the Masters semi-finals in Monte Carlo, losing to Grigor Dmitrov (4:6, 6:2, 6:7 (2:7)).
The tournament in Barcelona will be held from 18 to 24 April.