The Phoenix boss offered his full support to the departing winger ahead of his move to the Championship.
"I wish Luke all the best at Portsmouth and have told him if he needs anything to pick up the phone," said Greenacre.
Greenacre stressed that transfers of this nature validate the operational strategy of the Wellington club.
"His move again proves our club has the leading pathway in the country for nurturing and developing young and emerging talent," said Greenacre.
He affirmed that player ambition remains a core element of the institution's culture.
"And it's part of the Phoenix Way to help our players live out their dreams of playing abroad," added Greenacre.
The English coach previously noted that the decision was ultimately evaluated at the executive level.
"I'm obviously disappointed to lose Luke.
He's an integral part in terms of us playing young players and I really wanted that opportunity to work with Luke because I think we can get him to another level," said Greenacre.
Greenacre explained how player sales support the financial sustainability of the club.
"But obviously the powers that be decide whether it's the right move for the player and the right move for the club, and we've decided it's the right way to go," said Greenacre.
He emphasized that selling top prospects allows for essential reinvestment.
"It buys into what we're doing.
We want to help produce young players and if we can make a profit from them and reinvest that into the club and to the owners, that's what we want to do.
