Klopp and Wagner have known each other more than 25 years – Wagner was best man at his wedding – after being team-mates at Mainz but more recently have found themselves on opposite sides of the technical area.
Wagner was manager for Huddersfield’s brief stay in the Premier League but lost all three matches against Liverpool.
Now he brings the Canaries to Anfield for a fourth-round tie on Sunday looking for a favour he knows he will not get from his long-time friend.
“We had already conversations about it. He asked me for massive rotation. I told him that doesn’t help, obviously,” said Klopp of Wagner’s request to face a weakened team.
“It’s cool to have the game. When he worked at Huddersfield, he watched a lot of games here in the stadium, when they didn’t play he was here, and now he’s back.
“We didn’t see each other for a long time, the next time probably would have been in the summer, so now it’s good to catch up and to lock horns again.”
Wagner has a 40 percent win ratio since taking over at Carrow Road last January but, after a sticky patch between September and November when his side won just twice, he has got them back in form.
Wednesday’s defeat to fellow Championship promotion-chasers Leeds was only their fourth loss in 16 matches.
“(He did a) really good job but a really difficult job. I think the start of the season was really good and then they lose more or less their offensive department and that’s when they struggled a bit,” said Klopp.
“Now they are in touching distance of the play-off spots and they obviously have big games coming up.
“The Championship season itself is already pretty intense but if you have a longer FA Cup run in it, it’s obviously very similar to a very successful Premier League season with international football or something like that, because of the amount of teams in the league and the amount of games you have.
“I follow it as much as I can because I’m just interested in everything he is doing.”