Much as both the individuals concerned try to make light of it ahead of Wednesday night's Champions League meeting between AC Milan and Barcelona, there exists an ugly grudge between Pep Guardiola, the head coach of the European champions, and Zlatan Ibrahimovic, the man who helped return AC Milan to the status of Italian champions.
The enmity certainly burns strong enough within Ibrahimovic for him to have devoted a large part of his autobiography, published in Swedish last week, to the way his 2009/10 season at Barcelona, which began with a €60 million (Dh303m) transfer from Inter Milan and ended with a loan deal to AC, turned sour.
That was due, by Ibrahimovic's vivid account, to Guardiola's failings.
If the Barcelona coach has been characteristically quiet in his responses to Ibrahimovic's criticism, it cannot help but unsettle him that such a prominent footballer is on the attack, or to be reminded that Barca's Ibrahimovic experiment will be remembered as a costly, if rare, blemish on an outstanding managerial record.
Perhaps translations of I Am Zlatan, whose first edition sold out almost immediately as it hit the bookshops of Sweden, have yet to be presented to Guardiola. Or perhaps he would simply rather not study them. Ibrahimovic won a league title at Barca, just as he has at Inter, Juventus - as far as he is concerned, the Juve titles of 2005 and 2006 stand, despite the verdicts after the Calciopoli trials - and now Milan. But his adventure in Spain was unlike his experience in Italy, he says.
At Barca, "the players were all like school pupils. The world's best team, the likes of [Lionel] Messi, Xavi stand and nod at what their coach says. I thought it was silly. If a coach in Italy says 'Jump', the players say 'What do you mean? Why do we have to jump?'
'I didn't fit in. Not at all."
Ibrahimovic likes to style himself the nonconformist, on and off the field, and his fiery analysis of what went wrong at Barcelona has the stubborn aspect of his character at its heart.
"You should know," he tells readers of I Am Zlatan, "that ever since I was in Malmo [the city where he grew up] my philosophy has been to do things my way. I don't care what people think.
"I like guys who drive through the red lights, if you know what I mean. At first at Barca, I stood and nodded at Guardiola like the rest, like in school - or like I should have done in my school days. I hardly even yelled at my teammates any more. I became boring.
"Zlatan wasn't Zlatan any more."
So what should the real Zlatan be? "I need to be free as a bird on the pitch. I'm the guy who wants to make a difference."
At Barca, after a productive start in terms of goals and his adaptation of the well-tuned routines and combinations of Barca's passing games, the big bird had his wings clipped, or so Ibrahimovic feels: "Guardiola sacrificed me. That's the truth. He blocked me."
Turn the pages of I Am Zlatan and the story has a clear thread of envy.
Ibrahimovic resented the status of Messi in the evolution of Guardiola's plans. Around the start of 2010, with Barcelona thriving, problems began when "Messi started talking. Messi is an amazing player, though I cannot say I know him very well," Ibrahimovic says.
"He came to Barcelona as a 13 year old, was brought up in their culture. He has no problem acting like a schoolboy. But in that team it is all about him.
"After I arrived I was scoring more goals than he had. So Messi went to Guardiola and said 'I don't want to play on the wing any more, I want to play in the middle of the attack'. Guardiola became pathetic, and he switched to something more like a 4-5-1 formation with me just ahead of Messi.
"That's when I began to move into the shadows. He did it for Messi and it meant I didn't get to play my natural game."
By most reckonings, Messi's role at the centre of Barca's attack has been a stunning success. He has won two Ballons d'Or since the switch. But in the mind of Ibrahimovic, it indicated the shortcomings of Guardiola.
"He shouldn't have adjusted the team for one individual. Why had he bought me if that was the case?"
Ibrahimovic wanted to ask Guardiola that, again and again. He felt he had scant opportunity. "I tried to confront him, look into his eyes. He would look away."
The Swede's "friends from the Malmo ghetto" even offered "to come over and beat people up, destroy things". Fortunately, Ibrahimovic thought better of the suggestion. But by May that year, he sensed, rightly, he "was no longer welcome in the club".
Tonight, he has his first opportunity to express, perhaps more eloquently through his actions than his words, whether this serial rebel really does have something the school prefects do not, and if Guardiola may indeed have made a mistake.
UAE TV: 11.45pm, Aljazeera Sport