Arsène Wenger makes no pretence about it: the knowledge gained from eight years of working with Robin van Persie will be of only limited use when he sends his defenders out to face the Dutch striker at Old Trafford on Saturday. It is the measure of Van Persie's special quality, the Frenchman pointed out this week, that no amount of analysis can guarantee a way of keeping him quiet.
"A little bit," Wenger said with a shrug when asked whether those years of familiarity had helped him to prepare his players for the task of nullifying a player who left Arsenal for Manchester United on the eve of the new season.
"But Robin van Persie's great quality is that in a fraction of a second he understands where to go," he said. "You can talk and talk and talk but a defender has to read that at the same time. His speed of analysing the little pockets around the box is absolutely exceptional. They know him well because they played against him in training. But in the game itself it's a question of timing. How quickly will you read it as well as he reads it?"
Although generous in their assessment of his former captain, Wenger's words were delivered with an understandably sombre tone. The financial coup in collecting £24m for a player who had cost £2.75m eight years ago could not mask the lingering disappointment at losing a man he had turned not just into the most potent striker in England but also into a leader whose 30 goals in the last campaign not only made him the Premier League's top scorer but were the reason that Arsenal are competing in the Champions League for the 15th year in a row.
Nor could Wenger deny that Old Trafford is providing a suitable setting for the gifts of the man he calls the "most efficient" striker in the Premier League, a judgment backed up by statistics showing that Arsenal's shots-to-goals ratio has deteriorated since his move, while United's has improved. He was not surprised, he said, that Van Persie had adapted so quickly, with nine goals in his first dozen competitive matches.
"At Manchester United he has good players around him and Robin is very intelligent around the box," he said. "His runs are fantastic, his technique is absolutely amazing, so I'm not surprised. They are a lot of the time in offensive positions, so with his intelligent runs, of course he will take advantage of that."
Each word of that testimonial is a pinprick of pain in the heart of the manager and supporters of Arsenal, where Van Persie arrived from Feyenoord in 2004 as a 21-year-old winger who had scored 15 goals in 61 Eredivisie matches but had yet to make his full international debut. He was known to have great technical gifts but a reputation for an uncertain temperament had trailed him since his schooldays – when, as he has said, he spent as much time serving suspensions as behind a desk.
Van Persie was 16 when Sir Alex Ferguson got wind of the talented young forward at Feyenoord and sent Jim Ryan, then his reserve team manager, to Holland to take a look. Unfortunately the boy got himself sent off.
"Jim said he was a fantastic talent but he felt that he was a little immature," Ferguson said on Friday. "At 16 we're all immature but we didn't progress it and he went to Arsenal."
Gradually, and in the face of a spate of injuries that interrupted his early years in north London, Wenger tamed his excesses without curbing his spirit and turned him into a player of consistent menace. To the surprise of many the manager made him captain after Cesc Fábregas's departure in the summer of 2011, and the role suited the one-time rebel. He took his responsibilities seriously, becoming something of a father figure to the younger players.
"You would think that one of the parts of my job is to have a positive influence on people's lives," Wenger said. "When you manage to do that, you are always kind of satisfied. You want to try and have a positive influence on the people you cross in your life. In this case I think my influence was not too bad."
Somewhere along the line Van Persie grew up and stopped being an irritating presence on the pitch, allowing his imperious carriage, balletic movement and lethally economical finishing to become a focal point of any match in which he took part. In terms of his Old Trafford predecessors he brings something of the cerebrality of one former United striker, Teddy Sheringham, and the menace of another, Cristiano Ronaldo.
He signed a four-year contract with United a week after his 29th birthday, bringing him an estimated £240,000 a week – about £60,000 a week lower, it appears, than the bid tabled by Manchester City. It was a decision made, he said, after listening to "the little boy" inside him. "That boy was screaming for United," he said.
He made his debut as a second-half substitute in the defeat at Everton with which his new club opened their league season but then scored with his first shot in a United shirt as they beat Fulham next time out. His first hat-trick, against Southampton, came in September, averting his manager's wrath after he had failed with an audaciously dinked penalty attempt. Three weeks later a more orthodox execution from the penalty spot supplied the winner at Anfield. Last month he scored his first goals for United in Europe, against CFR Cluj, the Romanian champions.
"He's settled in well," Ferguson said, "He's a mature player and his start to the season has been fantastic. I can't say he's better than I thought he would be because that's why we bought him. His goals tally last season was fantastic. Hopefully that continues here. If you get a couple of strikers who score 25 goals [a season], you're in the ball park to win something.
"It's not easy coming to a club like this. Some take time but in the main we've been lucky. [Dwight] Yorke was unbelievable in his first season. And in recent years it's been easier because we've had a more consistent thread to the club."
Give or take the occasional Jordi Cruyff and Raimond van der Gouw, Ferguson has done well with his Dutch captures. Three of Van Persie's predecessors settled in quickly and made a significant contribution to the club's success in recent years. The first, Jaap Stam, arrived for £10m and won a Premier League winner's medal in each of his three years at Old Trafford before what Ferguson later admitted to have been a hasty and unwise decision to sell him to Lazio. Stam shared his last campaign at United with Ruud van Nistelrooy, who arrived from PSV, scored 23 goals in 32 league games in his first season and stayed five years, scoring 150 goals in 219 matches in all competitions before leaving for Real Madrid. The third, Edwin van der Saar, overlapped with Van Nistelrooy by a season and spent six years earning himself a place among the ranks of United's greatest goalkeepers.
The parallels between Van Persie and Van Nistelrooy are obvious, not least in their international records: 35 goals from 70 appearances for the elder of the two, 31 in 71 so far from the younger. Van Persie is joining the club at the age at which Van Nistelrooy left it but, if his excellent start can be maintained, then he stands a chance of making a similar mark on United's history.
Ferguson's only problem is how, with Wayne Rooney and Javier Hernández also in his squad, to deploy his abundance of resources. "I'm trying to work out how I can use the three of them together, plus Danny Welbeck, but it's a difficult one. We did it at Newcastle" – a 3-0 win in which Van Persie, Rooney and Welbeck started, although none scored – "but we can't do it every game."
Despite all those goals for Arsenal, followed by a lucrative transfer to a club who can be virtually guaranteed to mount a credible challenge in every available competition, not everything has gone right for Van Persie this year. In the Euro 2012 finals he made little of the anticipated impact as Bert van Marwijk's star-studded but unco-ordinated team failed to make progress past the group stage, his sumptuous consolation goal in the 2-1 defeat by Germany – a characteristically fierce drive from the edge of the D following a smooth dribble in from the left wing after he had been moved wide to make way for Klaas-Jan Huntelaar – providing his only moment of distinction.
Does Wenger regret his absence from the Arsenal squad? "That's very difficult to answer because at the moment I'm focused on doing well with the players I have," he said. "To start to think about how much we miss him will not help us."