Cash has applied for a Polish passport to help quicken up the process of playing for their national team despite previously clinging onto hopes of a surprise England call-up.
Smith said, "You ask people and if they've got a family line whether it's Polish blood or German blood or whatever and they want to go and do that then I certainly wouldn't stop them.
"England picked four right-backs for the Euros so it's certainly going to be tough to get in that!"
Cash, meanwhile, was serenaded at Chelsea in midweek with the 3,000 Villa fans chanting: "Matty Cash, the Polish Cafu!"
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