The 29-year-old played three matches for Serbia at the tournament in Russia, and was given extended leave to go on holiday following his country's elimination.
Matic joined the pre-season tour on 22 July and trained with the squad for the first time two days later, but played no part in Wednesday's 1-1 draw with AC Milan in Carson, California.
Following Saturday night's 4-1 defeat against Liverpool in Ann Arbor, the manager confirmed that Matic had left the tour to undergo surgery.
“Matic arrived from the World Cup, holiday, direct to surgery because something happened in the World Cup,”
said Mourinho.