Contepomi was named as skipper by Marcelo Loffreda on Friday and is relishing the challenge of facing the elite players from the four home unions at the Millennium Stadium.
"It's a dream match. A unique game," Contepomi said.
"Nobody will be able to take away the dream of entering history, because this is the first time the Lions will play against a national team in the United Kingdom and I think it may never happen again."
Loffreda described the game as "one of the most important matches in Argentina's history".
Meanwhile, Federico Mendez has announced he is considering retiring from the Pumas after this match.
"It's a possibility," Mendez explained. "I'll talk to the head-coach and then I'll see what I'm going to do.
"I've been playing internationally since 1990 and my body is feeling the effort."