Sources have told ESPN that United are in advanced talks to appoint Rangnick as the club's interim manager until the end of the season.
Sources have told ESPN that Rangnick emerged as the outstanding candidate during interviews for the United role following the sacking of Ole Gunnar Solskjaer last week.
"Unfortunately a good coach is coming to England and Manchester United," Klopp told a news conference on Friday.
"That's how it is. He's a really experienced manager who built two clubs from nowhere with Hoffenheim and RB Leipzig. He's done a lot of different jobs in football but his first concern is being a coach and that's his best skill.
"United will be organised on the pitch and that's not good news for other teams [in the Premier League]. Ralf will quickly realise that he has no time to train because United play all the time, but a really good man and outstanding coach will come to England, if it happens."
Liverpool face Southampton in the Premier League on Saturday and are eight points clear of United in the table.
A first league meeting between Klopp and Rangnick could come when Liverpool host United in March.
"We faced each other when I was a very young coach when he was at Hannover and he called me the 'young manager at Mainz'," Klopp said.
"They got promoted [to the Bundesliga] and we didn't, so he owes me something maybe. He's very well regarded in Germany and rightly so."