Onuoha was sent off for the incident, but referee Graham Salisbury admitted after the game that he was wrong to do so - and the FA seem certain to rescind the card.
Rovers physio Baz Windle said: "It was a clean break and the doctors decided to put it in a pot.
"He'll be in plaster for three months, then we can start his rehabilitation but he will play again this season."
City boss Stuart Pearce said: "In defence of Nedum, he is not the type of person who would go out to hurt anybody.
"He is distraught at what happened and feels he has let the side down."