I'd reckon there is around £40,000-per-week being dangled in front of his representatives.
Celtic simply cannot compete with the wages available even to average players in the English Premier League, let alone strikers who have proved themselves at Champions League level and forced their way in to the fringes of the England squad.
So, it comes as no surprise the new contract they offered Gary in October has been rejected.
I don't think it would come close to what will be on offer down south.
Celtic cannot be criticised for this. The TV income available to every club in the English top flight is so much more than they can generate, even with a Champions League run, which you cannot budget for every year.
And we don't need to be reminded what happens if you live outwith your means.
Neither should there be any criticism levelled at Celtic for not making Gary an offer which would make him the top earner in the squad.
I'd imagine the guys who would still be ahead of him got their deals when the wage structure was higher, or came to the club on Bosmans when there was competition for their signatures, or were transferred from clubs where they were earning even more than they were offered at Celtic.
Gary has become a real asset, but the club cannot destroy its wage policy for one man as this would have serious repercussions, not least in the dressing room.
I am sure Celtic have done the best they can with regard to an improved contract.
And, let's be honest, whether Gary signed it or not, if a high enough bid comes in, he will be allowed to leave. Celtic have said this.
So, why not accept it now and make everyone happy?
I don't think he will, but I still believe it would be worthwhile for Gary to stay at Parkhead until the summer, at least.
Not for the sake of the club, not for the manager who gave him his big break, or even for the fans who adore him – but for himself.
If he goes before the window closes a week tonight, he will be passing up the chance to play in the last 16 of the Champions League and to become one of very few players who can claim to have won a Treble with Celtic.
That's something he might regret when he looks back on his career, especially if the level of club trying to entice him to England is such that winning trophies and playing in massive European games are unlikely to be common occurrences.
The experiences which lie in front of Gary, if he stays at Celtic, will help him develop into an even better player, and may even strengthen his hand when it comes to negotiating personal terms with whichever club he eventually joins.
And let's not kid ourselves. While so much is made of players "needing to test themselves in England", it is the money on offer down there that is the real attraction.
I left Celtic for Chelsea in the early Seventies, and the gulf between what you can earn in Scotland and what is available in England is now much, much more than it was back then.
That's not a criticism of Gary, or any other player who takes the chance, if it comes along, to move south.
Football is their livelihood and, of course, they will go to wherever the big money is.
But he is still young, and those big offers will still be there five months from now.
Neither am I concerned the price Celtic could hold out for then would be substantially reduced, just because he would have only 12 months of his contract to run.
If he can continue to knock in the goals the way he has been, and show up well in the games against Juventus, there may be even bigger clubs with even deeper pockets interested in him.
By a week tomorrow, we will know if he is a Celtic player for the remainder of the season, and I really hope he is.
Without him, I'd still back Celtic to win the Treble, but there is no denying they would have more chance of getting past Juve and into the Champions League quarter-finals if he is leading their attack.
He can go now, and grab the money.
Or he can stay and win trophies, be part of a historic couple of European games and then leave with the best wishes of every one of the fans whose backing has helped make him the player he has become in his time at Parkhead.
For his own sake, I hope it's the latter.