The midfielder, who has started Man United’s last four games, withdrew from the Serbia squad ahead of games against Romania and Montenegro on Tuesday due to a back injury.
Matic underwent surgery in the summer to treat a long-term problem and has struggled to regain full sharpness since returning to the United squad.
And according to ESPN‘s Rob Dawson, Jose Mourinho faces a nervy wait to see whether the former Chelsea midfielder will be fit in time for a crucial trip to Stamford Bridge after the international break.
Luke Shaw has also pulled out of international duty having sustained an injury, once again stripping him of the chance to play for England, but the exact extent of the knock is unclear.
Marouane Fellaini did not train with the Belgium squad on Tuesday due to a cold but is expected to recover in time for internationals against Switzerland and the Netherlands.
11 players in total are going away with their countries over the next week or so. Mourinho, ahead of a massive game against Chelsea, faces an anxious wait.