The pair, who played together for both the Crusaders and New Zealand, will be in opposition in Sunday's European Champions Cup semi-final.
Carter, 34, will line up for French side Racing 92 at the City Ground if he recovers from a leg injury.
"When he's on top of his game, as we saw at the World Cup, there's probably no better," said Mauger.
"He's a fantastic footy player," he told BBC Radio 5 live. "He's pretty resilient, he's always worked very hard to be the best that he can be and that's why he has been one of the best the game has ever seen.
"He's a pretty complete footballer, but we'll be looking to test those skills this weekend."
Carter's evolution
Mauger feels Carter's game has developed over the past decade, due in part to a run of injuries that left him questioning his future in the sport.
However, Carter returned to spearhead the All Blacks to a second successive World Cup victory last autumn.
"Like any player, he's evolved," added former centre Mauger. "He's had to re-package himself over the years, especially with injuries, but I think he's come back a better player.
"I know the All Blacks have put a lot of time into keeping him in the game, because there were some dark times when he was thinking about throwing it in."
Mauger feels Carter's game has developed over the past decade, due in part to a run of injuries that left him questioning his future in the sport.
However, Carter returned to spearhead the All Blacks to a second successive World Cup victory last autumn.
"Like any player, he's evolved," added former centre Mauger. "He's had to re-package himself over the years, especially with injuries, but I think he's come back a better player.
"I know the All Blacks have put a lot of time into keeping him in the game, because there were some dark times when he was thinking about throwing it in."
