Rangnick is yet to be officially confirmed as manager and United travel to Stamford Bridge on Sunday afternoon for a heavyweight clash.
Thomas Tuchel's side are 12 points clear of United at the top of the Premier League and Rangnick will be watching, not just for United though.
Havertz faces a late fitness test and it's clear former RB Leipzig boss Rangnick is a personal fan.
He told Sky Sports back in 2020: "I have no doubts whatsoever that he will become a sustainable success and that he will become one of the top players in the next two or three years.
"Maybe, he will need a couple of weeks to get adjusted because he has a fantastic family background.
"I know that because I was also trying to convince him to join us at Leipzig, but he was completely dedicated to Bayer Leverkusen.
"He's one of those players where I don't see any weaknesses in his game. He's the type of modern Johan Cruyff - he can score goals and he can provide assists."
Cruyff is regarded as one of the greatest footballers to ever live and his incredible technique has been unmatched for years.
It's high praise for Havertz who is still in the infancy of his career at the top level.
The 22-year-old arrived from Bayer Leverkusen in a deal worth £72 million and he failed to find a place under former manager Frank Lampard.
Tuchel's arrival at the start of this year has seen him given more opportunities in a number of positions, including up front.
He scored the winner against Manchester City in the Champions League final back in May and Rangnick is a fan of his versatility in attack, but stresses his best football is played through the middle.
Rangnick continued: "He can play as a nine or nine-and-a-half. I don't see him as a winger but in the central area of the pitch, he's extremely valuable.
"I have no doubt that this transfer will prove to be a success story for Chelsea and for Kai.
"His best position is either a No 10 or in a 4-3-3, he can play as one of the two offensive No 8s in midfield.
"He's very versatile and almost the complete offensive midfielder with a complete 360-degree radar to score goals and provide assists.
"It's only a question of time for the whole league to see what kind of player Chelsea have signed."
Tuchel is expecting more from Havertz in his second season and he's no longer filling in as the main striker, following Romelu Lukaku's return.
He's made 17 appearances in all competitions so far this campaign, scoring four times and assisting twice.
Do you think Kai Havertz will prove to be a successful signing for Chelsea?
Featured Image Credit: PA Images
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