Liverpool shattered the British transfer record to sign the 22-year-old from Bayer Leverkusen for a reported fee of around £116 million.
Wirtz has so far failed to live up the hype and is yet to register a goal or an assist in a competitive game for his new club.
Former Man United and Bayern Munich midfielder Hargreaves has now weighed in on the situation, urging Slot to find “the right balance.”
Hargreaves said: "They were so good last year, they looked like they should blow everyone away. This year, they have signed some really good players, but Wirtz, when you pay that money, you try to get him in.
“But actually, that midfield three was the best in the league last year. You couldn't get better than Ryan Gravenberch, Alexis Mac Allister and Dominik Szoboszlai.
“All of a sudden, you spend that money on Florian and you've got to play him really. They've tried to get him in, and then Szoboszlai has played at right back, and I just think the balance is off. Ibrahima Konate has made a few mistakes, which we didn't see last year.
“I just think it's a balance issue. They've got two new full-backs; the addition of Wirtz, Alexander Isak. You've got to think that they've got so many great players. It goes back to the Arsenal-Arteta thing; you've just got to get the balance right on the game."