Along with being arguably the finest centre-back of his generation, Leonardo Bonucci is the central character in one of the more remarkable anecdotes starring a modern footballer.

In October 2012, Bonucci, his wife and their then three-month-old son were accosted by an armed robber at a Ferrari dealership. The masked man pointed a gun in the Italy international's face and asked for his watch.

Clearly unhappy with this state of affairs, Bonucci punched his assailant to the floor and promptly chased him from the scene – forcing the thug to flee with an accomplice on a scooter.

According to Gazzetta dello Sport, as Bonucci took the law into his own hands, the retreating villain shouted: "What are you doing? Are you mad? I'll shoot you."

Now AC Milan have agreed a deal for the shock signing of the 30-year-old, this tale of frankly unhinged bravery is worth consideration in terms of his Juventus departure. It is impossible to imagine having arguments with Bonucci is an enjoyable past-time for Juve boss Massimiliano Allegri or, indeed, any human being.

The reported breakdown in relations between Bonucci and his coach – first at Palermo in February and then in a subsequently denied half-time row that apparently involved Paulo Dybala and Andrea Barzagli at June's Champions League final – must lie at the root of a transfer that threatens to shake Italian football to its foundations, because there is no logical reason for Juventus to feel they benefit from strengthening a domestic rival to this extent.

Bonucci was an established hero of the Juventus faithful, a symbol of their unbroken spell of current dominance and the club's defiant recovery from the Calciopoli scandal. He arrives in Milan on the back of six consecutive Serie A titles.

Alongside Barzagli and Giorgio Chiellini, he formed a formidable defensive trio in front of the great Gianluigi Buffon. The celebrated quartet were undoubtedly approaching the end of their celebrated days in unison but Bonucci was their youngest member. Even allowing for Allegri's growing inclination to field a back four, his departure can only hinder Juventus on the field.

The Old Lady have managed to absorb the blows of losing Carlos Tevez, Arturo Vidal, Paul Pogba and Andrea Pirlo over recent years because of their almost immovable foundations. Those foundations have now had a chunk ripped out of them.

Italy's major clubs have habitually done business with one another over the years but this somehow feels different to anything in the recent past. 

Look across Europe to see previous examples of rivals weakening rivals and Manchester United's signings of Andy Cole and Robin van Persie from Newcastle United and Arsenal respectively spring to mind, along with Bayern Munich's more recent harvesting of Borussia Dortmund and the acrimony that came with Barcelona favourite Luis Figo becoming Real Madrid's first Galactico.

But in all of these instances, the beneficiaries were the more dominant force and the selling club put up varying degrees of an almighty stink.

Only Figo, like Bonucci, could reasonably claim to be the best in the world in his position and, yet, Juventus have let this happen. The speed with which Milan have pulled off this heist is faintly disorientating.

For all their ambition under new ownership, perhaps the Rossoneri's recent struggles – sixth, seventh, 10th and eighth-place finishes over the past four seasons, a crushing distance away from the champions – are what convinced Juventus this move should not be too directly damaging.

Signing Andre Silva, Ricardo Rodriguez, Hakan Calhanoglu, Andrea Conti, Franck Kessie and Mateo Musacchio, while retaining stellar young talents like Gianluigi Donnarumma and Alessio Romagnoli is all well and good when your first European assignment of the season comes against Universitatea Craiova – the fifth best side in Romania.

The gap between Milan and Juventus is vast but it is one closed considerably by Bonucci, who knows a thing or two about forcing daunting odds in his favour. Just ask a certain would-be watch thief.