Casillas is enjoying life in Portugal’s Primeira Liga after ending his 25-year association with Real Madrid in July.
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The 34-year-old Spain international signed a two-year contract with the option of a third, and while he is happy in Porto, a move to the United States is of interest.
Responding to a question in a live Q&A session via his official Facebook page, Casillas said: “The game has grown a lot over there and that’s brilliant to see … Would I play there? Why not?”
Casillas added: “I’ve signed for three seasons here and I intend to complete my contract here.
“Porto is a new challenge for me and I hope I can live up to the expectations at this great club.”
Casillas has conceded four goals in 10 Primeira Liga matches for second-place Porto this season. He also has helped the Portuguese giants to second place in Champions League Group G.