The Foxes have secured Facundo Buonanotte on a season-long loan from Brighton.
Cooper, who was previously at Nottingham Forest, admits he does not have enough options especially for his frontline.
“We know where we are with the level of some of the areas of the squad and we’ve just got to keep going,” Cooper told BBC Radio Leicester after the loss to Lens.
“We’re all crying out for some fresh blood, especially the players. Today it showed that.
“We had players playing out of position. Let’s hope we can strengthen sooner rather than later. In certain areas of the pitch, we’re desperate for it and have been for a while.
“We need to make the squad stronger. That is most important. It’s natural when you step up to the Premier League from the Championship that you have to strengthen a lot if you want to give yourself a chance of succeeding.
“I don’t think it would be right to put a number on it, but it’s certainly more than a couple. The players want that as well. It gives everybody a boost.
“They’re asking. They know. Some of them have played in both leagues and they know the difference. That’s what the desire is. Let’s hope we can make that a reality.”
On the Brighton talent, Cooper said: “The position he plays. From day one, we’ve said we needed players in certain positions and certain profiles because players have played out of position most of pre-season.
“He’s a young player but he has Premier League experience. He’s one the club’s identified. We’re really pleased he’s here. It was a pity that it wasn’t done quickly enough for him to be involved today, but fingers crossed he will train on Monday and we can plan with him.”