Ahead of Thursday's Europa League match against Shamrock Rovers, Redknapp said: "He needs another.
"He has already had one but there is still a problem with him. It's a blow."
Writing about his injury on Twitter, the 24 year old midfielder said: "Thanks for the supportive msgs [messages], I will do everything I can to be fully fit asap. Once the op is complete I will have a better idea of time."