When Bayer Leverkusen wasn't winning matches during the Pre-Season games the sign was there for them to have gotten a replacement for Ten Hag instead of taking the big risk to let him handle 2 matches before sacking him, the bold step is commendable by the management as Ten Hag could not get a win in his first two matches the best thing to do now is for them to make a serious signing before the transfer window closes they should get more players and get a better manager to revive the team.
I don't think judging any coach based on preseason is the right thing to do, because preseason matches are not always serious. A preseason match is just a way of warming up players. So, despite not winning any matches in preseason, it is not the right decision to sack a coach.
Ten Hag is a new coach at Leverkusen, and the club may have done thorough research before deciding to appoint him.i know it won’t be easy for Leverkusen this season, and part of the reason is that they don’t have enough quality players in the squad. We can compare this season’s Leverkusen team to last season’s and even the one from two seasons ago.
If Ten Hag was opportune to be coaching same squad that Alonso coached last season and last two season, the situation might not be this bad he might have seen at least one win from the two matches they have played so far.But as you've said, the best thing for them to do now is to enter the transfer market and quickly make some good signings before the window closes.