Football (it's Euro 2016) is a team sport so players are important but it's also very important how they play together as a team. Sometimes there are teams with average players that win competitions because they help each other much more than teams with star players (example: Leicester this season).
I don't know if you can model this taking in account single players, even if their performance in previous games could be an indicator about the strength of the team. We will see soon how the model fares.
I'm no statistician but "soon" seems unlikely; wouldn't you need a lot of results in order to judge how good these predictions are? I'd like to know if the model can use data capped at any time period, so that matches from the past can be judged against what the model would predict.
If they have data for the last 10 years they could use the model to predict thousands of games. That would start to be statistically significant for anybody.
However, I'm no statistician myself too but if the goal is to predict only 12 results how do we evaluate the predictions of the model? There should be a difference between 0 and 12 successes.
I don't know if you can model this taking in account single players, even if their performance in previous games could be an indicator about the strength of the team. We will see soon how the model fares.