The robbery took place at the former Manchester United centre-back's home in southern Rome, with luxury watches and jewellery taken.
Smalling was forced to hand the items over to three armed men before they left the house.
Police, who were called to the house at 5am local time, are investigating the incident, in which no-one was harmed.
Smalling is understood to be shocked by the incident but is now calm after the situation was brought under control.
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