"He has to become a man suddenly, he can no longer be the kid with promise, and he's showing it," Maradona said on Thursday.
"He's fast, concentrated, totally committed, he knows the chance he has," he added at a news conference in Buenos Aires ahead of Saturday's match in Rosario.
"We've been heaping responsibility onto him...Since I've been coaching Messi, since I've been watching him (train), this has been his best week."
Messi has yet to transfer his brilliant club form for Barcelona to the national stage for Argentina, whose fans hope to see him inspire his country to victory in his first official match in the city of his birth.
He had barely entered his teens when he left Rosario for Barcelona after no club in Argentina could afford the hormone treatment he needed if he was going fulfil his huge promise.
Brazil have not lost to Argentina in four matches since the teams' last meeting on Argentine soil, a Juan Roman Riquelme-inspired 3-1 victory in Buenos Aires in 2005.
Overrun by a counter-attacking Brazil in the 2005 Confederations Cup final, a 2006 friendly in London and the 2007 Copa America final in Venezuela, Argentina managed to stop the rot in a 0-0 draw in last year's qualifier in Belo Horizonte.
QUALIFICATION BALANCE
A World Cup without Messi, widely regarded as the world's best player, and Argentina seems almost inconceivable.
Yet Argentina can ill-afford to drop points if they are to remain on course for the 2010 finals in South Africa.
They are precariously placed in fourth place in the South American group, the lowest automatic qualifying berth, five points adrift of leaders Brazil.
The team finishing fifth after the remaining four rounds in the 10-nation group have second chance to qualify with a two-leg playoff with the fourth-placed team from CONCACAF.
Maradona, beset by injuries, is giving defender Sebastian Dominguez a debut alongside his Velez Sarsfield team mate Nicolas Otamendi and a first competitive start to Napoli midfielder Jesus Datolo after he scored on his debut in last month's 3-2 friendly win in Russia.
"Our idea is to go out to strangle Brazil," Maradona said.
"We will attack them down the wings with Maxi (Rodriguez) and Datolo, and with (Juan Sebastian) Veron through the middle...(Carlos) Tevez and Leo (Messi) will cause trouble for Brazil's two centre backs.
"They have some big names, but whoever plays we know we are going into battle, whatever yellow jersey goes by we will have to chase it."
