The All Blacks skipper was this week singled out by All Blacks assistant coach Steve Hansen described as the greatest New Zealand flanker of all-time. Quite an accolade in a country that gave the game Michael Jones, Josh Kronfeld, Ian Kirpatrick, Graeme Mourie and Waka Nathan.
The 23-year-old Rees knows the enormity of the task ahead of him at Auckland's Eden Park on Saturday and, just like Haskell, he can't wait to put himself to the ultimate back row test.
"There's no getting away from the fact that he's been the best openside in the world for the last few years - probably the best back rower, full stop," said Rees.
"He keeps getting better. It's fairly daunting going up against him for the first time, but that the sort of thing I want to aspire to.
"I'm fully aware of the challenge and it's not going to do be any good if I sit in my room quaking. Then he'd have the upper hand on me straight away."
Rees has nine caps compared to Haskell's six, but they have both arrived in New Zealand with some pretty good endorsements after helping McGeechan's Wasps side win the Guinness Premiership final.
As Haskell attempts to take over the England mantle that belonged to his recently retired Wasps team mate Lawrence Dallaglio he has been described by one legendary All Black as being "a bigger, faster and stronger Dallaglio".
Those words of warning to New Zealand fans and players came from Craig Dowd, now forwards coach at Wasps and will no doubt have pricked up the ears off McCaw's back row colleagues, Rodney So'oialo and Jerome Kaino.
"It was great to finish playing alongside Lawrence with him winning the Guinness Premiership final because he is one of my heroes," said Haskell.
"I loved his sayings, his mentality and we will miss that, even though he won't be too far away."
He won't be in New Zealand, though, to help his two young colleagues through their first tilt at the All Blacks,