The 26-year-old sustained the injury in the first half of the contest and was visibly distressed before being stretchered off the pitch.
Advertisement
Advertisement
Supporters at the Campos de Sport applauded the Spaniard as he received medical attention and was subsequently taken off.
Following further examinations, Racing confirmed the severity of the injury in an official statement released on Monday.
The development has sparked renewed criticism of Real Madrid manager Jose Mourinho across Spain, with attention turning towards the circumstances surrounding Mantilla's injury.
It remains unclear whether the Portuguese tactician will publicly address the controversy as Racing assess their defender's recovery prospects.