The England winger was expected to be back in six weeks, giving him a month to impress Fabio Capello ahead of England's World Cup squad announcement.
But Redknapp thinks even that might be pushing it.
"He's had about nine scans," said Redknapp. "The latest scan showed he has torn a little bit more fibres of the groin area. Until they heal it will take a bit of time.
"He's still a fair way away. He has worked as hard as he can to be fit, but getting to the bottom of what his problem was has been difficult."