"Other than saying it was time for younger players to take over, Matic did not state any other specific reasons for quitting," said Matijasevic.
"We've got several players who are over the hill and we realise that some of them may call time on their international careers in the next year or two."
His departure marked the end of a disappointing two-and-a-half year run at Old Trafford, where he arrived in a swap deal involving Henrikh Mkhitaryan from Arsenal.