The 34-year-old told Racing 92 he could not play in Sunday's Champions Cup semi-final with Leicester as he had to attend to a family matter in Argentina.
But he was pictured in the United States socialising with members of French football club Paris St-Germain.
In a statement, Racing said the suspension is a "precautionary measure prior to launching legal proceedings".
In Castrogiovanni's absence, the Parisian side beat Leicester 19-16 and will meet Saracens in the final on 14 May.
Italy prop Martin Castrogiovanni has been suspended by his club after he was pictured in Las Vegas last weekend.