Morgan, who has scored 123 goals in 224 appearances for her country, has appeared at every Olympics for Team USA since Beijing 2008 and won gold at London 2012.
The two-time World Cup winner has not scored in her past eight games for San Diego Wave after recently recovering from an ankle injury.
"Today, I'm disappointed about not having the opportunity to represent my country on the Olympic stage," posted Morgan on social media. "This will always be a tournament that is close to my heart and I take immense pride an time I put on the crest.
"In less than a month I look forward to supporting this team and cheering them on alongside the rest of our country."
Former Chelsea boss Emma Hayes will take charge of her first tournament as the USA manager, and has opted for Trinity Rodman, Jaedyn Shaw, Sophia Smith and Mallory Swanson as her main forward options.
"It was a tough decision, especially considering Alex's history and record with this team, but I felt I wanted to go in another direction and selected other players," Hayes said.
Women's football in Paris begins on 25 July, with the gold-medal match taking place on August 10.
The United States, who won bronze at Tokyo 2020, are drawn in Group B where they will face Zambia, Germany and Australia.
Thompson-Herah, who is hunting an historic triple double at this year’s multi-sport showpiece, is among 15 top international female athletes that have been signed to bolster the brand.
The 31-year-old Jamaican National 100m record holder and the fastest woman alive over the distance, is joined by United States soccer player Alex Morgan, the Olympic gold medalist and two-time World Cup winner who is expected back on the pitch after being sidelined by an ankle injury.
Hawaiian surfer Carissa Moore, the first winner of the Olympic gold medal in women’s short board surfing at the Tokyo 2020 Games, is also among the list of sporting heroes representing Dior, which belongs to luxury conglomerate LVMH Moët Hennessy Louis Vuitton, a premium partner of the Paris Games.
In addition, the brand has tapped swimmer Emma McKeon, Australia’s most decorated Olympian with 11 medals in total, and Japanese fencer Misaki Emura.
There are six Italian athletes: fencers Rossella Fiamingo, Alice Volpi and Arianna Errigo, and Paralympic fencers Beatrice “Bebe” Vio Grandis, Andreea Mogos and Loredana Trigilia.
From France, Team Dior will include boxer Estelle Mossely, skateboarder Louise-Aina Taboulet, fencer Sara Balzer and judoka Clarisse Agbégnénou, who hopes to reap a second Olympic gold medal after her win at the Tokyo Games.
Dior and LVMH had previously revealed three joint ambassadors –gymnast Melanie de Jesus dos Santos, wheelchair tennis player Pauline Déroulède and Para-cyclist Marie Patouillet, who was among the group of athletes that carried the Olympic torch on the red carpet at the Cannes Film Festival on Tuesday.
A series of portraits of the participating athletes will go on show at Le Café Dior in La Galerie Dior at the brand’s historic flagship in Paris from July 24 to September 9.
