Pre-season matches are only limited to testing the strengths of each team and a place to show talent for young players, whatever results are obtained in pre-season matches will not affect the team's reputation. They are just having fun before the game officially starts, the coach can also determine how appropriate a player is to be included in the core squad.
It won't be long before the Champions League will roll again, teams that are still in the stage of looking for new players are still moving in the transfer market in order to strengthen the depth of their squad. This season's Champions League will be far more competitive than the previous season, several teams that were absent from last season's Champions League have revived this competition. They also come with a well-prepared squad and of course will present a more fierce competition to the most favored teams to win this championship.
I think reputation is not damaged, but also it could be doubted a bit. Think of it like this, if one great team ends up playing against not so great team and loses, that is going to end up with the great team being doubted until they prove otherwise.
Same goes for champions league elimination phase as well, there are some good teams playing against some bad teams and there should be something very important to note about the fact that they are going to end up facing some issues there, if they do end up failing to win, people will doubt that team and not going to end up getting the recognition they deserve. Doesn't mean they will be bad after that, they could get better but the doubt will be there until they prove otherwise.