Kopp insisted that the players were given the green signal only because they were "fit" and the medical staff is now working to get both Dominik Szoboszlai, who is nursing a hamstring injury, and Alexander-Arnold back on the pitch as quickly as possible.
"We work in a high-performance area where, if you had the same injury, you are fit after three days and [the player] is fit after four weeks because they have to sprint and stuff like this," he said.
“We always try to catch the earliest moment but unfortunately when we catch that moment, nobody speaks about it. Like with Macca (Alexis MacAllister), or recently with Diogo (Diogo Jota), that’s a job we have to do. But the last decision is then always by the player and if we always listen only to the player then they would play after two weeks and then it’s a real problem.
"So the boys were, at the moment when they played, they were fit. But the situation told us then differently because it happened again. We will never know if it would have happened anyway or if it just happened because there was something before. Very, very unlucky and unfortunate, absolutely, but I had that a couple of times in my time as a manager, not only here. It is not great, but nothing else.
"It says nothing about the quality of anybody but in the world we are living in there is always [talk about] the medical department. We have to bring the boys as back as soon as possible but never sooner than they are ready.”