Fellaini, who was left out of Belgium's squad for the international break by coach Roberto Martinez, posted a photo of Instagram to show his signature look was gone.
Fans and teammates seemed shocked at the Belgian's fresh cut.
Fellaini played the full 90 minutes for United in their 3-1 derby loss away to rivals Manchester City, despite recently returning from a groin injury.
The Red Devils will next face Crystal Palace after the international break.
