“First of all, I think he is a great player and he has still not finished his career,” the Dutchman said.
“I do not know how his situation is and I need to respect that situation. That’s not my problem. But even when we get one time the possibility that Rooney is an option for Everton, I’m very pleased.”
As the season wore on it became increasingly clear United's all-time top scorer was surplus to requirements at Old Trafford, 13 glittering years after moving from Goodison Park in a £25million deal.
Throughout the summer talk of a return to the club where a 16-year-old Rooney announced himself to the Premier League with a stunning last-gasp winner against Arsenal continued.
“Remember the name, Wayne Rooney,” boomed Clive Tydlsley; the piece of commentary synonymous with the forward's breakthrough moment.
While the Rooney name has not been forgotten – nor is it ever like to be – it does not carry the same weight it did a few years ago. The last couple of campaigns have been hard for the 31-year-old who was reduced to the role of substitute under José Mourinho last season.
Rooney was not able to fall back on his well-publicised Plan B of playing in midfield. Despite United's glaringly obvious lack of depth in that area he showed nothing to suggest he possesses the attributes to run the engine room.
A shadow of his former self, it was clear he no longer served a purpose at Old Trafford. Where once he dominated, charging around and dictating play, he shambled about last season causing more problems for his team-mates than opponents.
A tally of just five Premier League goals was the quantifiable evidence of a player who has declined badly from his 2011/12 peak of 27. So why did Everton re-sign an expensive player who is past his best and will expect to play more often than not?
It is easy to forget, given how long he has been in the public domain and how sharp his decline has been, that Rooney is still 31. Everton are signing a player who should have a couple of good years in him.
And he will have lots to prove. Returning to Everton was always going to be a dangerous game for Rooney. His legacy there was as a boisterous, fearless, irrepressible No.10 who became a beacon of hope for the club in the early days of David Moyes.
Some Everton fans, of course, could not forgive what they perceived to be Rooney's betrayal. “Once a Blue, always a Blue”, he famously said before becoming a red to join United in 2004.
Now he returns in the worst lull of his career and his powers diminishing rapidly. A gamble? Certainly. Foolish? Not necessarily.
Rooney will rejoin his boyhood club in a different role to the one he left. From rampaging centre-forward to a much more considered, nuanced No.10. There won't be the same explosive pace, goals or fits of rage. But his quality on the ball has not abandoned him; his record-breaking free-kick against Stoke City reminded everyone Rooney can unpick the lock when needed.
He is much more mature than when he left Goodison Park 13 years ago. Literally, he has grown from a boy to a man and he will know what is at stake with this move.
It's why, if he has the sense one imagines he does, he will play to his strengths and ensure he is still contributing, even if it's not the Rooney supporters recognise from before.
One element Everton fans will recognise is his fierce competitiveness. And it is this which will ensure he tries everything within his power to make himself useful.
This is the last-chance saloon for Rooney. The next step – assuming he is still desperate to continue playing when his contract expires in two years – is China or Major League Soccer.
If he wants to bow out of the Premier League gracefully and with the accolades and respect his fine career deserves then he needs to finish well at Everton.
The good news is the bar is low. No-one expects him to be a revelation. Not least when he will be competing with a number of exciting new signings to even start regularly. He could even find himself out of the starting XI if Swansea City midfielder and Everton transfer target Gylfi Sigurðsson joins.
But that is a good thing. With low expectations he should thrive. It's when and if fans start expecting him to breeze past defenders and rattle home from 20 yards there will be problems.
Naturally, there will be a clamour to see how Rooney does back with his first love. But once the first few games pass the hubbub around him will die down and the attention will be focused elsewhere. Even with Everton's exciting re-build the spotlight on Goodison Park pales into insignificance next to that trained on Old Trafford.
The other element is the Koeman effect. The former Southampton boss will take great personal pride in restoring Rooney to something like the useful footballer he should be for Everton. That will mean resting him for games which are not the Toffees' priority, taking him off when a match is won and sparing him if things aren't going so well.
Koeman was quick to talk up the prospect of signing Rooney whenever the subject came up last season. Now he has his man it is in the interest of both parties to make the move work.