The 24-year-old, who made a real impression with the Welford Road faithful after joining the club at the beginning of last season, is now all set to appear in his first World Cup following Marcelo Lofredda's decision to announce his final squad earlier than the August 14 deadline.
Lofredda, who will take over as Tigers head coach at the end of his World Cup commitments, has named Ayerza among 17 forwards in the 30-strong squad.
The long-serving national coach has selected a side packed with European and international experience, although both Federico Aramburu and Francsico Leonelli have been ruled out after failing to recover from injury.
The Argentines line up in Group D alongside Ireland, Georgia, Namibia and France and include six squad members who play their club rugby with Guinness Premiership sides.
P Albacete, O Hasan (both Stade Toulousian), M Ayerza (Leicester Tigers), A Vernet Basualdo (Alumni), H Agulla, N Fernandez Miranda (both Hindu), L Borges, I Corleto, J M Hernandez, A Pichot, R Roncero (all Stade Francais), M Schusterman (Leeds Tykes), F Serra (SIC), F Todeschini (Montpellier), M Ledesma, G Longo, M Scelzo (all ASM Clermont Auvergne), J M Nunez Piossek (Aviron Bayonnais), JM Leguizamon, G Tiesi (both London Irish), F Contepomi (Leinster), M Contepomi (Newman), M Durand (unattached), I Fernandez Lobbe, J M Fernandez Lobbe (both Sale Sharks), M Gaitan (Biarritz), R Alvarez (Perpignan), S Gonzalez Bonorino (Capitolina), E Lozada (CASI), L Ostiglia (Sporting Union Agen)