Gronkowski has clinched a spot in the Kentucky Derby starting gate with the colt's fourth straight victory.
Named for New England Patriots tight end Rob Gronkowski, the Kentucky-bred colt won the Burradon Stakes at England's Newmarket by 1 ¼ lengths on Friday.
For the first time, Churchill Downs is allotting one spot in the 20-horse Kentucky Derby field to a European-based horse.
Trained by Jeremy Noseda and ridden by Jamie Spencer, Gronkowski moved ahead of Mendelssohn on the European Derby leaderboard.
Mendelssohn will try to qualify for the May 5 Kentucky Derby through the main Derby leaderboard with a victory Saturday in the UAE Derby.
Another spot in the Kentucky Derby field is being allotted to a Japan-based colt.