Shelby Rogers played at Hertogenbosch, reaching the semi-finals before losing to top seed Aryna Sabalenka.
Despite a disappointing performance at Roland Garros last month, Halep has been performing consistently in grass competitions.
The Roland Garros this season was one to forget for Krejcikova as she was eliminated in the very first round by an unseeded player in the form of Diane Parry.
After the French Open, Coco Gauff only competed in the Berlin Open but her performance was exceptional.
Jessica Pegula is perhaps the most prolific American player at the tournament and she will be hoping for a positive performance.
The excellent British player Paul Jubb will attempt to surprise Australian Nick Kyrgios in the opening round of his home slam.
After a strong ATP Cup performance for Canada, Auger-Aliassime, who started the season ranked 11th in the world, soon rose to number nine.
The Spaniard could not display a good performance at Roland Garros, nor has she made any great bounds on grass so far.
Shapovalov had an incredible run to the Wimbledon semifinals last year, but the 13th seed is in bad shape going into this year's competition.
At the Bad Homburg Open, Anisimova did quite well to reach the quarter-finals but was defeated at that stage by Paula Badosa.