It was a phone call that threw former Mexico youth international Jazmin Aguas' fledgling career into limbo.

Aguas was in the Chivas club house in Guadalajara, where the 24-year-old from Escondido, California, had been working hard for four months to prepare for the start of the inaugural women's professional soccer league, Liga MX Femenil, on July 28.

Almost exactly a month to the day from the historic first game, Aguas' friend Clarissa Robles -- a current Mexico international also from California -- was about to board a flight to begin a career at Tigres in the Liga MX Femenil, but found out through her coach that no player born outside of Mexico's borders could be registered.

Robles called her friend Aguas to find out if she was in the same situation. Aguas ran down to find the Chivas staff to enquire. But after initially being reassured, it became clear that the Liga MX had closed the doors to Mexican-American players born in the United States, even if they are Mexico national team players.

When the formation of the league was announced in December, Liga MX president Enrique Bonilla had said that Mexican-U.S. dual nationals would be welcomed. But Article 8 of the league's rules indicates that there has been a reversal: "Only players born in Mexico can participate in Liga MX Femenil tournaments."

According to players, clubs appeared to have been unaware until late June and Club America was holding tryouts in Chicago just last week. Chivas manager Luis Fernando Camacho certainly didn't know when Aguas came to ask about her situation.

"(She) was part of our plans," Camacho said in an interview with ESPN Mexico. "We put in the paperwork and when they rejected it, we realized the rules we have to follow."

Like many young Mexican players, forward Aguas was naturally excited by the start of the women's league in Mexico. She finds it difficult to comprehend how she and others can pull on the Mexican national team shirt and not be allowed to play in the Mexican league.

"I think the rule is unfair, and it's sadly discriminating me and the other double nationality players," Aguas told ESPN FC from Guadalajara. "I find it sad that we were left out of this tournament. I simply don't understand how we can represent this country with pride and honor but can't play in the league. The whole idea of forming this league was to support women's soccer as well as the national team."

Aguas argues that for those girls who have graduated from college in the U.S. but maybe don't have opportunities abroad, the Liga MX was ideal to maintain fitness and form and push for places in the Mexico national team, creating competition for places in the process.

Mexican national team midfielder Olivia Jimenez -- who made global headlines in 2012 when she was nominated for the FIFA Puskas Award -- was part of Club America's preseason and only found out about Article 8 when the club tried to register her. The 25-year-old was born in the U.S. but raised in Mexico, adding an even more confusing layer to the rule. She's currently working in a printing business in San Diego and training on the side, which doesn't seem to be the ideal set-up for a current international footballer.

"In my humble opinion, I believe that it's absurd to be able to represent my country, but not be able to play in it," Jimenez told ESPN FC. "(The league) is a great project and I hope in the future they change (the rule) and I can play in my beloved Mexico."

ESPN FC has learned of at least three other players with Mexican citizenship, but who were born in the U.S., who were planning to play in the Liga MX Femenil this season and no longer can.

The rule certainly raises moral questions, and perhaps even legal ones.

The Mexican Constitution defines Mexican citizenship as those born in Mexican territory, or people born abroad and who have at least one parent who was born in Mexico or is a naturalized Mexican. But the Liga MX Femenil rule makes a distinction.

If the rule was applied to the men's league, Mexico internationals Isaac Brizuela and Miguel Ponce -- who were born in the States but raised in Mexico -- wouldn't be able to play in Liga MX. U.S. internationals and Mexican citizens Omar Gonzalez, Edgar Castillo, Joe Corona, Paul Arriola and a host of others couldn't have made the move south, either.

The closing of the Liga MX Femenil to those not born in Mexico hastened Veronica Perez's decision to step away from the game as a player and pursue a different career path, she told ESPN. Photo by Michael B. Thomas/Getty Images

Border clubs such as Club Tijuana are likely to have major problems in sifting through the eligible women players, with so many dual nationals -- like Mexican national teammate Jimenez -- in the Baja California region of Mexico.

The case of 29-year-old Veronica Perez is slightly different. The Hayward, California, native scored perhaps the most famous goal in the history of women's soccer in Mexico, when El Tri defeated the United States in World Cup qualifying in 2010. Soccer America described it at the time as "the greatest upset in the history of women's soccer."

Perez pulled on the Mexico jersey 89 times, but the closing of the Liga MX Femenil to those not born in Mexico hastened her decision to step away from the game as a player and pursue a different career path, she confirmed to ESPN.

"I've played 89 times for the Mexican women's team during the last six years, giving my best effort to represent Mexico with pride," Perez wrote on Twitter on June 30 in Spanish. "And now I can't play in the Mexican women's league? How weird. It makes no sense."

While Perez is exploring other careers and Jimenez is working in Tijuana, Aguas is completely unsure of her next move. She has options to play at universities in Guadalajara, and Chivas are allowing her to continue training at the club. But she knows "time is ticking" on her goal of playing professional soccer.

"It was heartbreaking because I had already signed my contract," she said. "I could see my level getting back and I was excited to represent one of the biggest clubs of Mexico in its first-ever women's Liga MX (Femenil season), but now it's over and who knows how long it will be until this rule is turned over, or if it will even get turned over."

Despite the heartbreak, Aguas remains convinced the league will be good for women's soccer in Mexico and will be supporting the Liga MX Femenil, probably fighting what would be a bittersweet feeling inside.

"As much anger I have or am upset over this, I do thank the federation for finally making this a reality," Aguas said. "It's a huge step and it's only the beginning of women's soccer here in Mexico.

"I'm excited for my fellow teammates and every single athlete that gets to participate in this league for the first time. I definitely wish them the best of luck and I hope they enjoy it because it's a beautiful experience."

The Liga MX didn't reply to a enquiry from ESPN FC as to why the rule was implemented.