The Hoops have averaged a point a game since Redknapp took charge immediately after their first meeting with United at Old Trafford in November.
However, he is convinced if anyone can drag Rangers out of the mire it is his old friend Redknapp.
"It is not easy when you are down at the bottom of the league," said Ferguson.
"Harry will be the first to admit that.
"It may have helped him if he had gone a bit earlier. But with Harry's experience and ability to judge players, he will have a better chance that most in that situation."