Petrucci was Italian, Pogba French, and both were learning English. At home they started teaching each other their own languages and cultures. Without knowing it, Petrucci was helping prepare Pogba for the next stage of his career.
When Pogba eventually moved to Juventus, he could already speak Italian and had an understanding of the country and its football culture. It was something his former housemate had helped him with simply because they were young friends trying to understand each other's worlds.
"When I was in Manchester, I played with Paul Pogba. We were in the same team," Petrucci recalled to Football Presse. "So for me, it was great to see him developing from a young player to a top player, to someone who in the end won the World Cup. I followed all his steps, and for me, it was satisfying to see how he was improving.
"We have a really good relationship. Not only because we were good friends on the pitch, but also because we were sharing a house. We lived together. So when we met, we spent a lot of time together. We were both very young and we felt that together we were growing.
"We were teaching each other something. I was trying to teach him the Italian culture, the language, and what we do, what we think in Italy. So when he went to Juventus, he was already prepared. Some of the first-team players, when Pogba arrived in Turin, were surprised by the fact that he was already prepared to speak Italian and understand the Italian culture and mentality."
There was nothing calculated about it. Two young footballers were simply helping each other adapt to life away from home.
"It was because we spent a lot of time together. And he did the same with me, talking about his own country. So we shared a lot of great memories together, great moments, and we tried to help each other to be better persons."
The friendship also gave Petrucci an unusually close view of Pogba before the physical transformation that would help turn him into one of Europe's leading midfielders. The talent was already there, but the finished player was not.
Pogba would leave United for Juventus, where his first spell in Turin would bring four Serie A titles, two Coppa Italia wins and a return to Manchester for a then-club-record fee. His career would eventually take him to a World Cup triumph with France, a second spell at United, another return to Juventus, a doping suspension and, most recently, Monaco. That comeback ended in August, when Monaco and Pogba agreed to terminate his contract after one season in which he made six appearances.
But Petrucci remembers the player before all of that.
"He was a really good player, you could tell from the start. He wasn't so physically strong, as he is now. We were living together in the same house, so we had a great connection and we were enjoying playing together.
"We had a really good team and in the two years playing together we won every competition. You could see the ambition he had but you couldn't always tell he would end up being so good. It wasn't until he went to Juventus and physically he became so strong, which made the difference for him."
That makes the language lessons even more revealing. Petrucci was not preparing a future Juventus player in any formal sense. He was simply teaching his housemate Italian while they both tried to make sense of life in Manchester.
"We were going to school together trying to learn English and when we were at home, I was trying to learn French and teaching him Italian. When you're in football, you have teammates from all over the world, so the more languages you know, the easier it is to communicate with everybody."
By the time Pogba reached Turin, that teenage education had unexpectedly become useful. Petrucci had given him an introduction to a country he would soon call home, while Juventus and Antonio Conte would provide the environment in which his physical and tactical development accelerated.
Petrucci was also growing up inside a Manchester United culture shaped by Sir Alex Ferguson. The teenager who had arrived from Roma found himself working around players he had previously watched from afar, while Ferguson's presence gave the academy players a clear understanding of what the club expected.
"Everybody called him boss because he was in control of everything. But to be honest, yes, he was the boss, but he was such a nice person and he made everybody feel happy and good at the same time.
"He was really demanding. He wanted everybody to perform, but not only on the pitch. He wanted everybody to be professional, to make as much as possible for the biggest club in the world. For me, it's something incredible to have worked with him and to have talked to him and to have learned something and improved, to be a better player but also a better person, because he was trying to push everybody to the maximum."
Ferguson's authority did not prevent him from making the younger players feel that they belonged. For Petrucci, that was one of the defining characteristics of the manager he encountered at United.
"He was speaking to everybody, from the top player to the last man, the youngest one. He considered everybody, and everybody felt part of the family.
"That's why the club always, when he was there, had amazing results, because he was great at doing this. But also he was an amazing person, really, really humble, really, really good guy."
It was an environment in which Petrucci and Pogba could develop alongside established internationals while competing with each other and learning from each other. Petrucci has previously described the reserve side they played in as a team that won virtually everything, while Pogba's development eventually took him beyond the level of the young players around him.
The irony is that Petrucci, who had left Italy to pursue his own dream at United, was helping a French teenager prepare for the country where that teenager would make his breakthrough.
"When we met, we spent a lot of time together. We were both very young and we felt that together we were growing.
"We were teaching each other something. I was trying to teach him Italian culture, the language, what we do, what we think in Italy. And he was talking to me about his own country.
"So we shared a lot of great memories together, great moments, and we tried to help each other to be better persons."
Pogba's first spell at Juventus became the defining launchpad of his career. Petrucci's own route was far less spectacular but took him through Romania, Turkey, Italy and Israel before his most recent spell with Messina. He never reached the Manchester United first team, but he remained part of the generation that came through Carrington alongside Pogba and others.
And when he looks back at those years, the remarkable part is not simply that he watched Pogba become a World Cup winner.
It is that, while they were just two young midfielders sharing a house in Manchester, Petrucci was already helping the future Juventus star feel at home in Italy.
Neither of them could have known it at the time.