It means the 17 times capped, Argentinean-born front rower will miss all of Aironi's pre-season warm-up matches and could be struggling to be fit for his side's historic Magners League opener against Munster in Cork.
Aironi are due to launch their pre-season campaign in France with matches against the ProD2 sides Mont de Marsan (11 August) and Bordeaux-Begles (14 August). They will also travel to England to meet Northampton Saints at Franklin's Gardens (27 August).
As well as having injury concerns over former Saracens star Aguero, Aironi will have to start their season without the services of Italian back row international Simone Favaro after he broke his wrist in a training session in Viadana.
There has been better news for the club in the return to training this week of another international back rower, Josh Sole, He underwent wrist surgery during the summer, while fellow internationals Pablo Canavosio and Paolo Buso have just spent two weeks each on the sidelines recovering from knocks.
International forwards Fabio Staibano, prop, and Andrea Benatti, flanker, are due to train for the first time with their new teammates next week after returning from injuries sustained last season.
Those players who toured South Africa with Italy in the summer are due to report back to their clubs on Wednesday, meaning the new squad will be complete for the first time.
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