Redknapp, who worked alongside Grant during his time at Portsmouth, is convinced that the 55-year-old is the man to drag his former club out of the relegation zone.
"I don't see why you'd give someone a job and then consider letting them go after three or four weeks," said Redknapp. "He has only just got there. That doesn't make sense. I'm sure he will do a good job there.
"I think he's there for the long-term. He'll do a good job there if he's given time."