Lennon picked up the injury against West Ham in December and has suffered a couple of setbacks since and Redknapp, although remaining patient, hopes the 22-year old can return to action soon.
"It must be frustrating for Aaron," Redknapp said. "He's desperate to get fit.
"We just can't get him right. He's had a few goes and broken down.
"He's been back to the specialist," he added. "We're taking our time again, building up his strength in the groin area.
"He works every day with the physios and hopefully he will be working back outside shortly, but he's not ready to join the group again. He's quite a way off.
"I hope he's going to be okay (for the World Cup)," he said. "I hope he'll play for us before the end of the season.
"He could suddenly see a bit of light and come back and if he does then he could be ready.
"Four or five weeks, we'll have to wait and see."