I'm confused. Why would a player have to leave?
From what I can see, there is room for him. 17 non homegrown players are allowed, we have 15 if you include Aubameyang. If we are talking about the 25 man squad, well we have 23 currently, Chukwuemeka, Vale, Casadei, they are all under 21, so we don't need to worry about that.
Are they talking about the actual positions on the pitch? That could be it, but Depay can play left, right or through the middle of the forward line. Mount and Pulisic currently play on the left, Havertz and Ziyech on the right, Sterling and Broja in the middle. Mount and Havertz are not wide forwards, so we don't really want to count either of them. I would rather have Sterling out wide and somebody else playing LW/LF.
I just don't see how there is no room for him in the squad.