Moreno suffers fractured tibia
The defender sustained the injury during the dramatic 2-1 defeat to Netherlands in the second round of the FIFA World Cup on Sunday.
Moreno went to ground at the end of the first half to make a challenge on Arjen Robben that left the Dutchman claiming for a penalty.
Those appeals were waved away and the Espanyol man had to be carried off on a stretcher and replaced by Diego Reyes.
"Hector Moreno has suffered a fractured tibia in his left leg, the medical services of the Mexican national team have confirmed," a statement on Espanyol's official website read.
The severity of the fracture is not yet known, but the injury means the 26-year-old faces a race to be fit for the start of Espanyol's La Liga season in August.
The news compounds a desperate day for Mexico, who led 1-0 with two minutes to go after Giovani dos Santos' strike, only for a Wesley Sneijder equaliser and then a controversial Klaas-Jan Huntelaar penalty in stoppage time to change the complexion of the last-16 tie.