Mexico winger Hirving Lozano has returned to club PSV Eindhoven to continue his recovery process from a right knee injury, sources have told ESPN's Katia Castorena.
Lozano's departure from El Tri's camp back to the Netherlands puts his Gold Cup availability in serious jeopardy.
The FMF has yet to officially announce Lozano's status for the tournament, which kicks off on June 15.
The 23-year-old winger picked up the injury in a Eredivisie match in April and arrived to the Mexico camp last week using a crutch.
Mexico coach Gerardo "Tata" Martino was hoping Lozano would be ready for the Gold Cup, but while Lozano was present at Mexico training on Wednesday, sources have indicated he is headed back to the Netherlands to continue his recovery.
The Mexico City native has been linked with a move away from PSV this summer, with Napoli mentioned, but his injury situation will likely have to be cleared up first.
Lozano's absence adds another negative to a difficult few weeks for Martino, with Javier Hernandez, Carlos Vela, Hector Herrera and Jesus Corona all out of the squad for various non-footballing reasons and the manager saying he'd never experienced players rejecting call-ups in his time with Paraguay or Argentina.
Former Pachuca player Lozano was a vital part of Mexico's attack at Russia 2018, scoring the winning goal against Germany in Mexico's opening game.
Mexico begins its Gold Cup campaign on June 15 against Martinique, followed by matches against Canada (June 19) and Cuba (June 23).
Mexico warms up for the Gold Cup with games against Venezuela (June 5) and Ecuador (June 9).