This morning, Reds fans awoke to the worrying news that the attacker's parents had been kidnapped in Colombia, and he was understandably left out of the squad to face the Tricky Trees.
Colombian president Gustavo Petro said on social media that Diaz's mother had been rescued, but his father remains unaccounted for, and authorities are offering a reward of £40,000 for information.
In Diaz's absence, Diogo Jota, Darwin Nunez and Mohamed Salah were on target in a routine win over Steve Cooper's side, and the former held up his teammate's jersey after breaking the deadlock in the first half.
Klopp was unsurprisingly asked about the ongoing situation in his post-game press conference, and the German confirmed that Diaz's mother had been found safe, but he found it "absolutely impossible" to focus on the on-field action.
"We heard last night late about it. Then we spoke to Lucho; [he] wanted to go home, [we] sent people with him, have people there who take care, there's part of families there as well so that's why they want to be together. Absolutely understandable," Klopp said.
"Then we got the news with [his] mum, which is fantastic, and since then nothing really. They work on it, clearly. By some distance we are obviously not the first people who get informed but we try to have knowledge of everything as much as we can, but we don't want to disturb in any way. [We're] not the important people there. We just want to support. That's it.
"So, yeah, good, absolutely good game and the question will come anyway, so I can give the answer immediately, the preparation was the most difficult I ever had in my life. Didn't expect that, was not prepared for it, I don't want to make the game bigger than it was, but it was definitely. We tried to help Lucho with the fight we put in because obviously we want to help, we cannot really help, so the only thing we can do is fight for him and that's what the boys did.
"Yeah, so how can you make a football game really important on a day like this? It's really difficult. I never struggled with that in my life. It was always my safe place, sometimes my hiding, as a player or as a coach, you are allowed during these 90 minutes just to focus on that and it was impossible. Absolutely impossible to do that.
"It was clear we have to give the game an extra sense and it was fighting for Lucho, then the boys put out the shirt and I was not 100 per cent prepared for that, to be honest. It was really touching but wonderful as well. So, yeah, that's it."
At first, Liverpool struggled to break down a resolute five-man Forest rearguard, but Jota tapped home into an open goal after Nunez was thwarted, and the Reds proceeded to squander several chances to add to their advantage.
However, slick play down the right from Salah and Dominik Szoboszlai ended with the latter cutting back for Nunez to rifle home into the roof of the net, before Matt Turner came out to meet a long Szoboszlai pass high up the field and horribly misjudged it, allowing Salah to round off the scoring.
Cody Gakpo also had an effort disallowed in the dying embers as Liverpool recorded a third win on the bounce, but Klopp still believes that there is "so much" room for improvement in future games.
"Yeah, I told the boys after the game the best thing you can say after a game like this [is] that we played really good and there's so much space for improvement," Klopp added.
"Still, that's obvious as well, the goals were fantastic, the patience we showed, the fluidity in a lot of moments on the ball, a lot of moments, the creative, the togetherness in how we connected with each other was really good."
Liverpool now return to EFL Cup action away to Bournemouth in Wednesday's fourth-round tie before tackling Luton Town at Kenilworth Road in the Premier League on November 5.