#2 Multiple match ban resulting in a suspension for Manchester United away fixture
Another possibility is Ronaldo being handed a multiple match ban, which might result in a big loss for Juventus as he would be then unavailable for, at least, one game against Manchester United.
Manchester United is the biggest test for Juventus in the Champions League Group this season, and having brought Ronaldo from Madrid for the sole purpose of winning the Champions League, his absence against a club like Manchester United might prove disastrous for the Italian Champions.