"The medical department told me he could have played against Chelsea, but I have heard the word risk too often so I decided no," said Klopp.
"I was very happy that it worked out. They told me if I gave him three days he would be perfect so today is the fourth day."
On Tuesday's opponents Derby, who have won only one league game so far this season, he said: "If I was the manager of Derby I'd tried to use this competition for the turnaround.
"There is no pressure on them. This game is a big opportunity. We watched as many games as possible of them and they created many more chances than they actually used. They have a good quality, very experienced manager."