Redknapp was full of praise for All Whites legend Nelsen's performance and compared his influence at the club to that of Scott Parker.
"I thought he was fantastic," Redknapp said. "I just think he is a great professional and a real good player.
"I couldn't believe I got him on a free. I felt it was an amazing player to bring to the club, he is a player I have chased for years.
"I have always thought he was top class, a great pro, a great trainer, a fantastic person.
"He has got a six-month contract. At the end of the season you have got to keep him here next year because he's worth his weight in gold just to have around for other people to look at the way he works, the way he trains, the way he behaves, his attitude.