Not
At
All
Croatia winning wouldn’t even be an upset
I doubt Croatia would win. Portugal has been defensively solid whereas Croatia is clearly struggling in that aspect. So, it won't be easy for Croatia to score.
Portugal problem is different. I think it was Forlan who analysed Portugal gameplay and said Portugal playing with traditional Number 9 is a problem.
Because Ronaldo remains stationary and barely leaves the central area, it gives opportunity to the opposition to have centre backs comfortably lock down the penalty box by having one defender mark Ronaldo while others remain unchallenged locking the box.
This creates an issue. Portugal mid aren't left with much build up space to work around and this results into Portugal attacks being funneled into predictable patterns. It's like a funnel effect.
Against teams struggling with defense or weaker teams, they can find a way out or even overwhelm them with pressing but teams with solid defense would definitely choke entire build up of Portugal attacks like Colombia did.
If Croatia can pull this off like Colombia did and score on counter then yeah Croatia win this.
But as I said, Croatia is struggling with defense itself.