"Nicky saw a specialist on Tuesday and had a re-scan," manager Steve Coppell told BBC Radio Bristol.
"After a lot of thought and consideration Nicky will have surgery on Wednesday."
It is a further blow to Bristol City's forward line who are already without Danny Haynes and on-loan Wolves striker Sam Vokes, who tore a hamstring in Saturday's defeat by Millwall.
Source: BBC Sport
Source: BBC Sport