Prior to linking up with the English outfit, the tight-head had enjoyed a successful spell with Super Rugby's Jaguares in his native Argentina.
Pieretto feature 17 times for the franchise on their run to the 2019 Super Rugby final, with only New Zealand heavyweights Crusaders denying them an historic title.
Part of Argentina's 2019 Rugby World Cup squad, Pieretto featured in the Pumas' pool stage victory over USA in Kumagaya as part of a renowned scrummaging unit.
He was also selected for the world's most famous invitational side in November 2019, representing the Barbarians against Fiji at Twickenham.
Nicknamed Kike, the prop has also represented his country at U19 and U20 level.