“Leguizamon has torn a muscle in his right thigh,” the Argentine Rugby Union said.
Isa, at 22 one of the youngest members of the Pumas squad, played at number eight in Argentina’s 54-9 victory over Georgia having not been a part of the match squad in their opening 26-16 defeat by New Zealand.
Leguizamon, at his third World Cup and a veteran of the Pumas team that finished third in France in 2007, was expected to come off the bench in the second half to refresh the team with his power and experience.
“We’re going to have the same physical fatigue (as against Georgia) and we know that if we want to qualify for the quarter-finals we must win,” captain Agustin Creevy said.
“We’re going (into it) with that mentality and we’ll try to play at a high level throughout the match to keep growing as a team,” the hooker said of the first ever meeting between the two nation at test level.
Argentina expect a large contingent of travelling fans to turn Leicester City FC’s stadium into an Argentine ground as they did in Gloucester where some 15,000 cheered on the team with their passionate chanting.
Soccer great Diego Maradona turned up at the ground to add his renowned motivational powers to the team.
Tonga’s Siale Piutau said the Pacific islanders would counter the Pumas’ perceived superiority by hounding them into submission.
“We have got this wolf pack mentality that is going to take on the Puma and that is how we are going into this game,” the centre said.
“It’s going to be an all-out battle, all-out war. We are just dying to get out on the field and get our howling on.”
Tonga are second in the group, one point ahead of Argentina after getting a second bonus point in their 35-21 win over Namibia. Their first bonus point came from losing by seven points to Georgia in their opener.
A win for Tonga would put favourites Argentina in serious danger of failing to reach the last eight.
“If we win, with a bonus point, it could take us somewhere we have never been before. We could make history here. This is going to be our 'final' for this World Cup,” captain and openside flanker Nili Latu said.
(Editing by Ed Osmond)
