Navarro trailed by a break in the opening set and served down 5-3 when Wozniacki slipped and fell on game point while chasing down a drop shot.
After taking a medical timeout, Wozniacki held serve to close out the set at 6-4 but won just one more game in the match and retired with a left knee injury at 4-6, 6-1, 1-0.
Navarro thus reached the second grass-court semifinal of her career, having made her first last year in Bad Homburg. This year, the rising American star has defeated Jaqueline Cristian and Peyton Stearns before facing down Wozniacki in the quarterfinals.
Wozniacki earned her first grass-court match-win since 2019 this week by defeating No.21 Elina Svitolina in the first round, and she followed up with a 1-hour and 24-minute victory over No.36 Veronika Kudermetova. She has been granted a main-draw wild card at Wimbledon, which begins on Monday.