Two-time Olympic medalist Laurie Hernandez and former world champion Morgan Hurd aren't part of the 18 gymnasts who will be competing in the upcoming U.S. Olympic Trials.

Four-time Olympic gold medalist Simone Biles heads the list of gymnasts who qualified for the trials, which will be held in St. Louis from June 24-27.

Hernandez was forced to withdraw after she said she hyperextended her left knee during warm-ups on Friday on the first day of U.S. Gymnastics Championships in Fort Worth, Texas. Hurd, who was making a comeback from elbow surgery, was unable to capture the form that led to her winning the world all-around title in 2017.

"The future is an unwritten place," the 19-year-old Hurd wrote on social media. "cannot express my gratitude enough to everyone for the constant love and support. i wouldn't be where i am or accomplish what i have without it. congrats to all the girls who made olympic trials, can't wait to watch you kill it!"

Hernandez was part of the "Final Five" squad that won the team gold medal in Rio de Janeiro in 2016. She also won a silver medal in the balance beam.

Hernandez, who turned 21 on Wednesday, returned to top-level gymnastics in February.

"Definitely heartbroken that this week didn't quite go the way I'd planned," Hernandez said on social media after her withdrawal in Fort Worth.

Biles won her seventh U.S. championship at the event.

Here is the list of the qualifiers for the Olympic Trials, according to USA Gymnastics:

Simone Biles, Spring, Texas/World Champions Centre

Skye Blakely, Frisco, Texas/WOGA Gymnastics

Jade Carey, Phoenix/Arizona Sunrays

Jordan Chiles, Spring, Texas/World Champions Centre

Kayla DiCello, Boyds, Md./Hill's Gymnastics

Amari Drayton, Spring, Texas/World Champions Centre

Kara Eaker, Grain Valley, Mo./Great American Gymnastics Express

Addison Fatta, Wrightsville, Pa./Prestige Gymnastics

Shilese Jones, Westerville, Ohio/Future Gymnastics Academy

Emily Lee, Los Gatos, Calif./West Valley Gymnastics School

Sunisa Lee, St. Paul, Minn./Midwest Gymnastics Center

Emma Malabuyo, Flower Mound, Texas/Texas Dreams

Grace McCallum, Isanti, Minn./Twin City Twisters

Riley McCusker, Brielle, N.J./Arizona Sunrays

Zoe Miller, Spring, Texas, World Champions Centre

Ava Siegfeldt, Williamsburg, Va./World Class Gymnastics

MyKayla Skinner, Gilbert, Ariz./Desert Lights Gymnastics

Leanne Wong, Overland Park, Kan./Great American Gymnastics Express