Mulumbu, who joined Norwich on a free transfer earlier in the summer, suffered the injury in last Saturday's friendly with Brentford and will be out for "several weeks", the Canaries said.
The former West Brom midfielder was to undergo an operation on Monday.
City boss Alex Neil said on the club's official website: "Unfortunately Youssouf has a fractured metatarsal which requires immediate surgery.
"We anticipate his recovery should take several weeks and this is something we will be able to assess further after the operation has taken place."
Norwich play Crystal Palace at Carrow Road on Saturday on their return to the top flight.
Source : PA
Source: PA