The Hoops currently sit 18th in the Premier League table, 10 points adrift of safety with four games left to play.
"I think this is a good club but when people say 'well, they'll come straight back up next year', it will be very hard to do that. Don't kid yourselves," said Redknapp.
"Whatever happens, the Championship is a tough, demanding league and you need players that are ready and willing to play Monday, Tuesday or Wednesday and then Saturday.
"You need the right characters if you're going to get out of the division and that is something that will have to be looked at very carefully."
Redknapp has past experience of gaining promotion to the Premier League, having guided Portsmouth to the Division One title in 2003.