From President Trump’s standpoint, a decline in the World Cup’s popularity due to Ronaldo’s absence would not be pleasant, and the same would be true for FIFA's.
If Trump were to implement his threat, he would, in essence, be Vladimir Putin's partner in crime in a war of aggression that violates international law.
Trump’s threat is purely economic, employing the power of coercion and open blackmail, to keep a ‘servant’ perpetually under subjugation from attaining economic independence.