The goalkeeper was ruled out of the trip to the capital after sustaining the issue in training on Friday.
Speaking to TNT Sports pre-match, Klopp said: “That Trent [Alexander-Arnold] is injured, Thiago [Alcantara] is injured, Dom [Szoboszlai] is injured, that was all clear. And yesterday in the last training session, minus one, Ali pulled out. That’s really not cool.
“But besides that, we have plenty of players coming back. I don’t know how many changes we made actually, I just made the line-up, so you have to tell me how many changes we have.
“We just try to figure out how can we be the worst opponent for Brentford, which is a big task, to be honest.”
Asked whether he knew the severity of Alisson’s injury, Klopp responded: “No, I don’t know that. It’s a muscle and we don’t know yet.
“We have to wait. How it always is, maybe tomorrow or the day after tomorrow we will know more.”