Barcelona had bad days recently. They lost a game in the Champions League against Monaco because of the mistake of their goalkeeper André ter Stegen and he was the reason for this result against Monaco.
Now it seems it is even getting worse because André ter Stegengot was injured hard and he lost the whole season because he can play for a long time.
Barcelona is now searching for a new goalkeeper to fill the place of André ter Stegen in this team.
Barcelona started this season very well, unfortunately Flick faced a huge problem, it will be very difficult to replace such a goalkeeper, and the biggest difficulty is that they lost Ter Stegen for the rest of the season. In the match against Monaco it was his mistake, but sometimes it happens, every person can make a mistake, yes it led to a defeat, but I am almost sure that this defeat will not be a big problem for Barcelona in the end, because they still have many matches in the Champions League. But the loss of the main goalkeeper is a huge problem for Flick.
Indeed, losing Ter Stegen is one of the problems faced by Barcelona, especially since Ter Stegen's injury is quite serious. But I believe Barcelona's performance will not decline even though they lose their main goalkeeper because Hansi Flick can handle it, especially since this season Barcelona has lost many of its key players but Barcelona's performance is still perfect where Barcelona has not been defeated in La Liga until now.