Ryan, 20, who has three months left on his Mariners contract, cannot officially sign for the fallen giant of Scottish football until 1 September under the terms of a transfer embargo imposed after it went into liquidation.
Hours after The World Game revealed the agreement, the Mariners released a statement detailing the arrangement.
The Mariners have outstanding debts to settle and are keen to cash in on Ryan – and Reading target Tom Rogic.
Rogic is suspended for Sunday's trip to third-placed Western Sydney Wanderers but Ryan will start for Graham Arnold's men at Parramatta Stadium.
It's understood Rangers – demoted to Scotland's fourth tier after going broke – is offering about $230,000 should Ryan impress coach McCoist.
Another European club has tabled a firm offer to snap up Ryan during this transfer window.
However, his future appears destined for the UK after Mariners General Manager of Football Lawrie McKinna discussed a proposed move with Rangers hierarchy on a trip last month to his native Scotland.
McKinna was a special guest in the directors' box for the Boxing Day clash against Clyde and has had discussions with McCoist.
"I was in Scotland over Christmas spoke with Ally McCoist about Mathew Ryan," McKinna said.
"It is a credit to Mat and to our Club that Ally was well aware of Mat’s ability and potential and immediately offered for him to join Rangers for a training spell.
"Mat is eager to take up the opportunity and we are sure he will learn a lot from the experience."
While away in Scotland, Ryan will miss Central Coast's Week 16 clash with Melbourne Victory at Aurora Stadium in Launceston on Saturday 12 January but is expected to return for the F3 derby against Newcastle Jets at Bluetongue Stadium on Saturday 19 January.
Having trialled with Tottenham Hotspur and West Bromwich Albion last August and being linked with Championship Hull City in November, Ryan has been courting an overseas move for some time.
And, on the back of his recent Australia debut against Korea DPR at the East Asian Cup qualifiers, his stocks continue to rise.
Rangers chief executive Charles Green has promised McCoist cash for new players after saying that a recent share issue was "the springboard for the rebirth of the club.
A recent share issue raised over $30 million, with $7.5m of that coming from fans.
The signings embargo means Rangers are unable to register free agents until September and will have to wait until the January 2014 to buy new players, but Green has promised a healthy transfer kitty when the restrictions are lifted.