Lavanini was part of the Chiefs academy this season and at 2m and 120kg was picked for the Pumas last week when veteran Patricio Albacete was injured and could not play the Springboks. He is only 20 but impressed in the Junior IRB world championships this season.
Another youngster, Pablo Matera, who played in that tournament, escaped any sanction after being charged with eye-gouging in the Pumas' narrow loss last week to the Springboks.
Argentina's talismanic captain Juan Martin Fernandez Lobbe has been cleared for the trip after a hamstring injury took him out of the twin tests with South Africa.
Without Lobbe, the side's morale and organisation slipped and they were embarrassed by an opening 73-13 loss in Soweto. Lack of leadership led to conflict within the group.
However, Mendoza and Lobbe's return will lift hopes for their trip to New Zealand and Australia.
With Lobbe, the Pumas should have a starting loose forward trio of Lobbe, Matera and Juan Manuel Leguizamon for the test in Hamilton.
However, they have lost backup loosie Leonardo Senatore, who has been banned for nine weeks for biting Springbok lock Eben Etzebeth in the fractious test at Mendoza.
Experienced lock Albacete has stayed at home to recover from injury but seasoned second-rower Manuel Carizza will tour along with Juan Imhoff and Juan Martin Hernandez, who have recovered from injury.
The 36-year-old Felipe Contepomi, who came out of retirement to play in midfield this season, is on the trip but may be spelled from the test in Hamilton.
Depth of players and year-round rugby are problems for the Pumas. The bulk of the squad play in Europe but instead of getting a break like their fellow professionals, they are needed for the Rugby Championship. The extra workload and travel must have an effect.
This season the Springboks have also picked players from Europe and some are playing there this weekend in the Championship bye round before the Boks play the Wallabies next Saturday in Brisbane.