IT is said that the most important relationship at any club is the one between the manager and the chief executive.

An astute operator in the boardroom won’t drive a club forward if the wrong man is in the dugout, and a good coach will find it hard to achieve if he is not supported from above.

They must work in tandem, understand where each other is coming from and share a vision for the future at all levels if a team is to lift trophies and a club is to thrive.

The lines of communication must be clear, the message coherent. Yet when it comes to transfer dealings the balance of power is intriguing.

At Rangers and Celtic, the respective rapports could be crucial sooner rather than later and Barrie McKay, Moussa Dembele and Kieran Tierney may well be at the centre of the discussions.

When the window closes next week, all three players will almost certainly still be in Glasgow. But, come the summer, some key conversations will have to take place in the corridors of power at Ibrox and Parkhead.

In the case of McKay, they are likely to be more straightforward. One day, the winger will leave the Light Blues and it is only a matter of when.

It won’t be to RB Leipzig this month, anyway. But if he continues to improve for Mark Warburton’s side then interest in his services from elsewhere will be firmed up and cash will be put on the table.

When that happens, it will be hard for Rangers to resist. After all, money talks.

McKay agreed an extension to his Gers deal last season and is contracted until next summer but he was relaxed when questioned about his future in midweek.

If no agreement can be reached to add another couple of years onto his Ibrox stay, then McKay will have to be sold at the end of the campaign. The 22-year-old is one of the few high worth assets in Warburton’s squad and Rangers can’t afford to allow him to enter the final 12 months of his deal and potentially walk away for a fraction of his value.

Gers fans would be sad to see him go, but the blueprint of signing or bringing through young players, giving them first team experience and then selling them on is the one that Rangers have to follow and McKay is the ideal example at present.

Across the city, it is the model that Celtic have used to great success in recent years as the likes of Fraser Forster, Virgil van Dijk and Victor Wanyama have helped the Hoops bank millions of pounds and the buy low, sell his strategy has paid off. It hasn’t always worked, but there have been more big hits than costly misses.

There came a point when Celtic just had to cash in as the will of the player and the money involved made a deal inevitable. It is Tierney and Dembele that now have the price tags around their necks.

Manchester United became the latest club to be linked with Tierney last week, while bidding for Dembele looks set to start at £20million come the summer.

But boss Brendan Rodgers will find himself in a different position than Warburton. Unlike at Rangers, there will be no financial requirement to sell, so will Celtic hold open the exit door?

For chief exec Peter Lawwell, the chance to bank tens of millions of pounds before a ball is kicked would be tempting and it would be no surprise to see Dembele, if not Tierney, leave at the end of the season.

All managers want to strengthen their squad rather than deplete it but when the pound signs are spinning there will be a realisation that the deals must be done.

It then becomes a question of how much of that cash is handed over rather than tucked away safely in the bank. Given the impact that Rodgers has made and the investment Celtic have made in him, the Northern Irishman undoubtedly has a strong hand to play and holds more cards than Warburton as the Rangers rebuilding job continues.

Come the summer, it could be necessary to talk. They will be the most crucial conversations of all between the men that calls the shots and the ones that picks the team.