Antitrust does not discriminate against a single company. If Apple is in violation of antitrust regulations either today or at some point in the future, regardless of how they got there, they would be subject to the same legal action. So no, theoretically speaking and practically speaking, this is not a risk.
That's not how it works in practice though. There's no US legal action against Apple, they can reap Billions and billions of dollars with their own monopoly before any action reaches them after Google and Facebook are crippled.
This is the big issue with targeted anti trust vs. industry wide regulation.
