Let me start with a pretty straightforward question: If you take out a vital part of an engine and then put it into a completely different one, would it work the way it used to? The answer is obviously, no. Although we cannot be certain what kind of a result we are going to get, we can be certain that the result will be different.
In football, you cannot just transfer players and expect them to show the same level of performance. To immediately achieve that, you would need his teammates and the gameplay they were following. Thus, if Galatasaray wants Diagne to perform as good as he did in Kasımpaşa, it needs to buy his playmaker, Mahmoud Trezeguet or assign a player in the Egyptian playmaker's role.
Although Diagne has played only two games for his new team so far, the pros and cons of his transfer are very clear. His finishing skills and aerial superiority will dramatically increase Galatasaray's goals, but there is also the danger of Diagne being the only option going forward. In other words, like Gomis last year, he will definitely become the target man, but if an opponent cuts off the connection between him and the rest of the team, Galatasaray needs an answer. Unlike last season, Galatasaray's opponents are well aware of the game Fatih Terim is trying to play and have taken further defensive measures. In this case, Diagne cannot perform well while having no time and space to play with the ball or not being supplied by his teammates.
The clearest example of this situation was set during Galatasaray's defeat against Benfica this week. Benfica played like an extremely typical counterpressing team, trying to stop Galatasaray while it was still building the game in defense. When it was defending on its own half, Benfica made sure that at least two defenders were marking Diagne. This was not the most elaborate plan I have seen, but it was enough to contain Galatasaray's offensive firepower. Apart from the blind crosses into Benfica's penalty box, Galatasaray was practically nullified by its opponent.
Now, given Galatasaray invested all of its transfer revenues on new transfers and focused on winning the championship again this season, it would be financially catastrophic if it cannot. But the Lions cannot beat Başakşehir in the championship race if they cannot score against properly defending teams because Başakşehir plays slow, organized football better than Galatasaray.
What Fatih Terim's team need is a maestro, like Trezeguet, who can transform Diagne into the new Gomis. Only with such a creative playmaker can Galatasaray score lots of goals in chaos. The primary candidate for this job is obviously Belhanda, but the Moroccan star needs to be convinced and taught to play in this way since his job has been being a hidden striker rather than a playmaker. If Belhanda can perform in that role, Diagne can be the Diagne Galatasaray wants.