O'Donovan scored 11 goals for the Mariners in his second season at the club earning interest from across the league.

Rivals Newcastle Jets and Western Sydney Wanderers have been linked with the 31-year-old and while Okon wouldn't reveal where he'd be playing next year, he said it wouldn't be in Gosford.

"It's already signed, sealed and delivered unfortunately," he said.

"We wish Roy well. He's been great value for us.

"He's a goalscorer and whichever team has him next season will be very lucky."

It will be all change at the A-League minnows in the off-season, with more than half of Okon's squad out of contract.

Talented goalkeeper Paul Izzo is understood to be heading home to South Australia to play for Adelaide United, while Fabio Ferreira has been linked with Western Sydney.

Others will be let go or have decided to go.

Okon - who will head to Europe on a scouting mission before the new season begins in October - has vowed to bring in fresh talent that will fit into the club's attacking ethos.

"We don't have the resources of other clubs so we need to spend our money wisely which I'm quite confident we'll do," he said after their season-ending 1-0 defeat at Melbourne Victory.

"We need to strengthen everywhere. We have potentially five visa spots available.

"We'll make sure that we find players that will fit into the way we play.

"We're onto that at the moment and with smart recruiting we can look forward to next year and really give it a crack to make finals."

Last year's wooden spooners don't know their final finishing position yet but have grown their points tally from 13 to 23 in Okon's first season.

He pledged to make the hard calls to swell that number next season.

"The ones that are out of contract or haven't committed somewhere else and we haven't signed yet - those discussions will take place now," he said.

"Tough decisions will be made purely on what's best for the football club."