The 30-year-old’s arrival from Stuttgart for around €19m (£16.2m) could be crushing after Liverpool missed out on big-money Moises Caicedo and Romeo Lavio to Chelsea this week.
Liverpool have seen a number of midfielders leave the club this summer, including Milner, who joined on a free transfer aged 29, but has since become a regular and Klopp credits him as the main reason for their success, including Premier League and UEFA Champions League glory. , in the last few years.
Endo has put pen to paper on a four-year contract and, despite being set to make his debut against Bournemouth on Saturday, Jurgen Klopp is delighted with his latest acquisition.
Jurgen Klopp said: “He’s late in his career and he’s definitely been underrated for a long time. It’s clear that he’s improved every year since he’s been on a proper football canvas.
“There’s no way anyone could (I think he’s 30), when you see him you’re like ‘is he allowed to drive a car?’ He turns into a real monster on the field.
“One of the biggest LFC legends of my time was James Milner, he came here when he was 29. I can tell you that without James Milner we wouldn’t have had the success we’ve had in recent years.
“Wataru may have a similar impact. The last week has obviously been difficult. But when you have a problem, you can stick to the problem or find a solution, I’m more than happy to have a solution.”
Liverpool had bids, well in excess of what they paid for Endo, accepted for Ecuador’s Caicedo and Belgium’s Lavia, but each opted to move to Stamford Bridge.
Jurgen Klopp had “absolutely nothing to say” but was adamant that bringing players to Liverpool had not become a more difficult task in recent months.
Overall, however, he highlighted how much more difficult recruitment has become due to the rise of Saudi Arabia and the eye-watering sums they are willing to pay for players.
Jurgen Klopp said: “I’m not sure it has anything to do with Liverpool. Everything is harder. There are a lot of things that are different, some clubs just do it differently and somehow it works.
“As a normal club, it’s really hard to catch them. That’s not my problem, it’s just the way it is. Moreover, Saudi Arabia did not make things easy. Infinite money causes a problem.
“It would be great if someone could find a solution. It was more difficult, but not convincing players to come to Liverpool. You just have to make sure you go for the right ones.
“I’m sitting here and I’m really happy with our transfer window at the moment. We’ll keep looking, we’ll try to make the best decisions for this club and we won’t use money or anything else as an excuse.”
Jurgen Klopp will again be without Spanish pair Stefan Bajcetic and Thiago Alcantara, but added that they are “really close” to returning to the first team after missing out on the pair in last week’s 1-1 draw at Chelsea.
While Jurgen Klopp was encouraged by the performances of summer signings Alexis MacAllister and Dominik Szoboszlai, he admitted Liverpool were slow out of the traps in their first game of the season.
He added: “We weren’t consistent enough in the way we wanted to play. What we lacked in the game was rhythm, especially in possession.
“We had 35% possession, which is a complete joke, it shouldn’t happen – it can happen against Manchester City on their special day and if that’s our idea, sit a bit deeper.
“It wasn’t our idea, but it happened. We have solutions for our situation, but they are not currently available.”