The Brazilian forward is set to join the north London club from Everton after a £50million deal was agreed.
And Antonio Conte will be expecting his new signing to put aside any animosity he still harbours for his star defender Romero.
Richarlison clashed with Romeo in both Everton's fixtures against Spurs last season after a feud that started on social media boiled over.
But the two are far from being the first rivals to find themselves eventually playing on the same team…
Andy Cole and Teddy Sheringham
The pair had been feuding for 25 years with Cole infamously claiming that he would rather share a cup of tea with Neil Ruddock, who broke his leg in two places rather than his former strike partner.
And the dislike stretches back to Cole's England debut back in 1995 which came just months after he joined Manchester United.
He came on only for then Tottenham forward Sheringham to snub his offer of a handshake and it's a gesture he never forgot.
Two years later, Cole was joined by Sheringham at United but the pair rarely spoke to each other and only had 10 joint goal involvements across more than 5,000 minutes of playing time together.
Lionel Messi and Sergio Ramos
There was no love lost between these two over the years when they were on opposing sides of El Clasico games between Barcelona and Real Madrid.
Back in 2010, Barca famously routed Madrid 5-0 in one of the most one-sided Clasico's ever where Ramos was sent off for a nasty swipe on Messi.
He was also then sent off in 2017 for a two-footed lunge at the Barcelona icon while he later publicly accused him of 'playing dirty' by messaging Atletico Madrid players before the Madrid derby.
However, they have since buried the hatchet after arriving at Paris Saint-Germain as Messi told Marca: "Now nothing.
"But at first it was weird after so many years of being rivals, being the two captains of Barcelona and Madrid, after so many Clasicos played, so many fights we had on the pitch.
"But all that is in the past and we have always respected each other a lot, no matter how much we have been rivals in those Clasicos. Having him as a teammate today is spectacular."
Romario and Edmundo
Both brilliant Brazilian strikers who became Vasco da Gama legends - but they also couldn't stand one another…
Back in 2000, Romario was re-signed by Vasco to partner Edmundo in attack for the inaugural Club World Cup to help the club compete with the likes of Man United and Real Madrid.
But the two forwards were already embroiled in a public feud after Edmundo had replaced his old friend in the 1998 World Cup squad.
In retaliation to his Brazil snub, Romario hung up a huge cartoon of Edmundo on the toilet door in his Rio bar - which didn't go down well!
"We never fought face-to-face," Edmundo told Desimpedidos in 2017, "we fought through the press. A time came that we were disputing a place in the Selecao, disputing championship titles, fighting for top-scorer awards, and even women in the nightclub.
"We arrived at the club and there was me in one corner and him in the other; I was prettier, I had the chat. So, we started to clash."
John Terry and Diego Costa
In an example that Richarlison and Romero might want to copy, these two clashed just months before becoming teammates.
Chelsea met Atletico Madrid in the 2014 Champions League semi-final in which Costa and Terry came nose-to-nose after a first-leg tussle.
However, Terry insisted the incident was long forgotten upon Costa's switch to Stamford Bridge: "First of all, his movement and his strength are really good - I was really surprised by it.
"I think everyone remembers the square-up we had in the first 10 minutes of the first leg of our semi-final game against Atletico Madrid last season, after which I thought, 'Fair play'."
Bruno Fernandes and Alex Telles
Fernandes was recently filmed launching an expletive-filled rant at Telles as the duo returned to pre-season training.
But thankfully for United fans, Fernandes was just ribbing rather than it be any left over anger from their time in Portugal.
Before they both arrived at Old Trafford, the pair were on opposite sides of the fierce Dragoes vs Leoes rivalry between Porto and Sporting Lisbon.
"So, me and Bruno have known each other for a while now," Telles told Inside United in 2020. "Bruno has always stood out wherever he played and he is undoubtedly our main player here today.
"We were rivals on the pitch [in Portugal] and today we're team-mates playing in the same team.
"I've said to him that at the time he was quite annoying to play against on the pitch, always wanting to win, obviously."