The Republican presidential nominee weighed in on the San Francisco 49er's decision to sit during The Star-Spangled Banner in a pre-game ceremony.
Mr Kaepernick said he will continue to sit out the national anthem until he sees improvements in US race relations.
Mr Trump called the quarterback's controversial stand a "terrible thing."
"I think it's a terrible thing, and you know, maybe he should find a country that works better for him," Mr Trump told KIRO radio in Seattle. "Let him try. It won't happen."
