Simplify the following text for a Grade 8 native English-speaking person.
Original: MatÃ as JesÃ s Almeyda ( born 21 December 1973 ) is an Argentine footballer who plays for Club AtlÃ tico River Plate , as a defensive midfielder .
Simplified: MatÃ as Almeyda ( born 21 December , 1973 ) is a former Argentine football player .