Manchester United not pursuing their interest in Kevin Strootman was one among the many puzzling moves, or lack thereof, made by David Moyes and Ed Woodward in the previous summer.
Strootman went on to sign for Roma in a move worth around £15 million and has been instrumental in the Italian club's terrific start to the season.
Moyes will now be hoping he had made his move for the Dutch international, but according to former PSV Eindhoven manager it is just a matter of time before Strootman moves to a club of United's ilk.
"Strootman is a pure professional," Advocaat told Algemeen Dagblad. "It frankly surprised me that he did not get to the absolute top last summer and was on the side a little.
"I do not think he will stay at Roma that long. If Kevin is at this level, he will be plucked away. And then it will be a team of the calibre of Manchester United."
The Strootman signing by Roma was not met with too much enthusiasm by the media in Italy, and the 23-year-old took a swipe at his critics after more than proving his worth over the past few months.
"Two months ago it was for many people still incomprehensible that so much money was paid by AS Roma for me," he said. "One week it's all perfect and a week later you can be nothing more.
"Also in Oranje [the Netherlands national team], we have in the last two international matches convincingly beating Hungary and Turkey, but if we dropped points against Colombia and Japan, we suddenly have nothing.
"At the World Cup in Brazil there will be all these criticisms, it is still the issues of the day. Yes, I have started well at Roma but many people who now say that I play so well in Italy have not seen a match of mine."
The reigning English Premier League champions have missed a player who can control things in midfield, with Marouane Fellaini yet to convince. Someone like Strootman to run things in midfield would be very welcome at United, and while a move in the January transfer window looks extremely unlikely, Moyes will definitely want to keep an eye on the midfielder in view to a move next summer.