In the summer Redknapp gave McClaren a coaching role at Loftus Road following ill-fated spells at Nottingham Forest and FC Twente in Holland.
McClaren quickly rediscovered his enthusiasm and subsequently took over at Derby, who he has guided into the thick of the Sky Bet Championship promotion race.
The Rams now lie just four points behind Redknapp's Rangers ahead of Monday's showdown between the two sides at the iPro Stadium.
"Coming here was good for him," revealed Redknapp.
"He'd been abroad and to Forest where it hadn't worked out, so to get back to coaching for a few months was something he could just enjoy with no pressure.
"He was always going to go back into managing but when you are a coach, everyone likes you, you aren't picking the team!
"Steve is cool and calm, a very good coach. He's well organised, knows the game and I enjoyed having him here.
"He's done a good job at Derby. For sure they are promotion contenders. We are all chasing Leicester at the moment, they are running away with it a little bit but you never know.
"There are about six or seven teams chasing them and Derby are one of them.
"It's a very tight division and it's going to go right down to the wire."
The Championship may be as congested as ever but Redknapp insists he is not thinking about the play-offs, and instead has not ruled out overhauling the Foxes at the top.
He added "They'e got a great advantage, you'd like to be in their position but it can change quickly with three or four games without a win so you never know.
"I don't think about the play-offs. I'm just concentrating on getting up automatically, that's what we want to do."
Derby are unbeaten in four matches but dropped points when they let a 3-1 lead slip to draw with Birmingham last weekend.
McClaren told Rams Player: "We've moved on from Birmingham - we have to.
"We came in last Sunday and had a team meeting, talked about things and we've now drawn a line under it and focus on QPR."