Looking at some highlights, I think Haksabanovic lines up in midfield if he comes. He seems to thrive in congestion.
SEAD HAKSABANOVIC | 2020 HIGHLIGHTS - YouTube
I only heard he is active on defense from that scouting report, but he seems to look like the left side of the diamond to me, or maybe the tip, but not one of the forwards... I say this as someone who is not too educated on tactics.
I think in a diamond 4-4-2, the left sided striker is the closest fit to the role he plays today. The major takeaway from his scouting report is that he likes to get the ball, aggressively dribble towards goal, and shoot. If that's the value he brings, you'd rather have him receiving the ball further upfield than he would from the left side of the diamond. Much more likely for him to create chances if he only has to dribble 15 yards than 50.