After three consecutive Premier League runners-up finishes, Mikel Arteta was left searching for answers.

What would it take to turn his Arsenal team into champions? The squad needed more depth. The mentality had to be tougher.

The club responded by signing eight new players. Yet the most important summer arrival may well have been the least conspicuous. Arteta turned to one of his oldest and most trusted allies: former Argentina, Paris St-Germain, Real Madrid and Manchester United defender Gabriel Heinze, who replaced outgoing assistant Carlos Cuesta.

Arteta and Heinze first met at PSG in 2001 under the management of Luis Fernandez.

"They were great boys," says Fernandez, who signed Arteta from Barcelona in January 2001 and Heinze from Real Valladolid six months later.

"It was a pleasure to manage them. What's great is they haven't changed. They're exactly the same today; loyal, hard-working people. When I see what they're doing at Arsenal, I'm very proud."

It feels highly significant that at this key moment in Arteta's managerial career, he turned to a figure who had performed the role of a big brother to him at PSG.

Arteta was just 18 when he left his homeland. He recently described his 18 months in Paris as "an experience that will stay with me forever, that shaped who I wanted to be as a player and ignited in me something to become a manager".

That PSG team was packed with star names and strong personalities. As well as Heinze, Arteta shared a dressing room with Ronaldinho, Mauricio Pochettino, Jay-Jay Okocha and Nicolas Anelka.

The first months were difficult for the shy, introverted Spaniard, despite the presence and support of his parents.

"It was very tough," remembers Yves Ribardiere, PSG's player liaison officer back then. "Mikel was living in a hotel that was quite basic. It was winter, the weather was cold and grey. He was in this small room and had a lot of time to kill. I used to stay with him to make sure he didn't get too down."

PSG's Spanish speakers also helped smooth the transition. Pochettino, then 28, took Arteta under his wing before Heinze arrived. "Mauricio was like a father figure," recalls ex-PSG defender Didier Domi. "Gabi was closer to Mikel's age and more like a brother."

Heinze is four years older than Arteta, but there was an immediate chemistry between the two. "They were together at training, and also spent time together away from the pitch with their families," recalls Fernandez.

"Gabi was a fierce competitor and always wanted to do better than his opponent. Mikel was more an elegant player with real technical qualities," adds the PSG legend who captained the club to their first league title in 1986 and won the European Cup Winners' Cup as coach a decade later.

Edouard Cisse insists the duo also had plenty in common. "They were both intense and passionate," explains Cisse, who partnered Arteta in PSG's midfield. "Gabi gave everything, even in training. He had to win. Mikel was calmer. But you knew not to rub him up the wrong way. He had that tough Basque edge."

Heinze took his notoriously feisty nature into management. Spells as head coach in his homeland with Godoy Cruz, Argentinos Juniors, Velez Sarsfield and Newell's Old Boys – and at Atlanta United in the MLS – proved tumultuous and short-lived.

In north London, Arteta is channelling Heinze's enthusiasm – and the Gunners are flying. "They're like two volcanoes," Cisse says. "One that erupts occasionally (Arteta) and one that erupts all the time (Heinze). With everything he has to manage, Mikel can't be shouting at his players constantly. You need help. Gabi will be doing that every day in training.

"It's a superb combination," Cisse insists. "Mikel has done a fantastic job, but he needs help to get his team over the line. Gabi, through his obsession with winning, can do that."

A rugged, hard-tackling defender who won league titles in France, England and Spain and played 72 times for Argentina, Heinze commands instant respect on the training ground, where he works primarily with the defensive players.

It is surely no coincidence that the best defence in England has become even stronger this season. "Gabi lives for football," says Fernandez, who remains in close contact with both Arteta and Heinze today. "He's always studying the game, and especially the work of the defensive players. These days you have a goalkeeping coach, a set-piece coach, it's important to have someone coaching the defenders too.

"You can always improve. Work on your positioning, tackling, distribution. That's where Gabi can help. When you have somebody of his experience telling you something, you listen. I'm certain he'll be improving those defenders."

Arteta has no hesitation entrusting Heinze with such key tasks. The pair share a bond that runs far deeper than football.

"The strength of a manager lies in his ability to surround himself with people he trusts completely," says Fernandez. "Mikel has made a great choice. Gabi is loyal. He's straight-talking, a real, sincere person and Mikel knows he'll support him every single day."

As Arsenal's season moves towards a thrilling climax, that trust off the pitch may prove as valuable as any signing on it.