The ex-Harlequins duo both tasted tournament glory back in 2003 - a year in which Leonard says England learnt from their mistakes in the lead up to their greatest global gathering.
"Is it vitally important that England win every one of these warm-up games?" asked Leonard at the official launch for the Help the Heroes Challenge between a Northern Hemisphere XV and their Southern Hemisphere rivals which takes place at Twickenham on December 3.
"It would be nice but if you look back at 2003 we didn't win all our games, we lost to France in Marseille albeit by one point but we still lost.
"And in that game we learnt a lot about players who were on the periphery of the England squad and which ones were going to come to the World Cup. As long as you learn from your mistakes, even a defeat can be turned into a positive.
"This England team have got to learn from their mistakes. It will make them a better team. It really is a case of whether they have enough time to learn from it as the World Cup is not too far away."
The nature of Saturday's defeat has caused plenty of concern throughout the English media but Greenwood believes their failure to turn a lions share of possession into points isn't as worrying as many critics are making out.
The 1997, 2001 and 2005 Lion admits his former skipper Martin Johnson will have been frustrated with the inability to put the game beyond Wales early on despite dominating field position and controlling the setpiece but he sees no need for a drastic rethink for the World Cup opener with Argentina on September 10.
"If England had not created any chances and lost then it would be time for panic stations," said Greenwood.
"There were five or six proper chances that were not taken which is frustrating but the wheel does not need re-inventing.
"You can get yourself in the right position, you can find yourself with all the territory in the world, but if you can't get across the blooming white line then life becomes very difficult.
"So there are some questions that Martin Johnson still has to resolve. But not being one-eyed, not wearing rose-tinted spectacles, I still, still believe that this is a very, very good England side, a very powerful England side.
"And when they get the confidence to play with ball in hand 20, 25 yards out, I feel as though they are going to score. I think they will suddenly turn themselves into a side that no-one, absolutely no one - not even New Zealand - will be comfortable about playing in a knockout stage."