This is really going to be a problem to Dortmund,it can even make them loose for Ajax.
Nevertheless,Dortmund had proved to play very well this season even when Haaland was absent,so we can see that Dortmund is in a good shape to win that match than Ajax.
and it looks like in the next match Dortmund will focus on attacking because a 4-0 defeat will make Dortmund want to take revenge on Ajax for the big goalless defeat that Dortmund must avenge.
Without Haaland, Dortmund are able to score, they can win, but I don't think they will be able to win 4-0 against a strong team like Ajax. If Haaland were in the team, maybe Dortmund could have scored 4 goals. But at the moment without Haaland, I don't think he can win 4-0. My guess is that Dortmund will win 2-1 or 3-2. However, winning the match against Ajax will not be easy. And of course you have to play attacking in this match. It will be difficult to win if you play defensively against a strong team like Ajax.