It's said in football that there is always a right time for a club to sell players. 

For example, when Sir Alex Ferguson knew it was time for Cristiano Ronaldo to move to Real Madrid, or closer to home, when Jota was offloaded by Celtic to Saudi Arabia for mega riches and Rangers sold Nathan Patterson to Everton for £16m.

That kind of messaging can be used up and down the football pyramid, at varying degrees of finance and levels of scrutiny that the world of the transfer window can bring. 

Phrases coined by Fabrizio Romano and the likes such as 'Here we go,' and 'proposals in place' have become synonymous with the modern footballing landscape. While there are plenty who dislike it - in fact - let's go a step further - detest it - there are plenty who revel in the excitement and unpredictable nature of player trading. 

That brings me to Celtic, the current three-in-a-row Scottish Premiership champions. 

Brendan Rodgers has made just two signings so far this summer - both of whom are goalkeepers. 

It was a position that urgently needed to be addressed with Joe Hart's retirement and the departure of Benji Siegrist, so in stepped former Premier League winner Kasper Schmeichel and Aston Villa youngster Viljami Sinisalo.

So far, at the time of writing, no out-field options have been added to the first team ranks, much to the dismay of a section of the Hoops faithful. 

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Perhaps, though, this summer was all about keeping the squad as firmly put together as possible. 

Derek McInnes said as much about his recruitment prioritise for Kilmarnock during the close season. The aim was not to lose players and maintain continuity with a squad that had performed so consistently well for him last term.

Maybe that's the sort of viewpoint Rodgers has with Kyogo, Reo Hatate and Matt O'Riley? 

We then come back around to the need of all clubs - aside from the elite - to sell their players are the right time in order to maximise their value.

So, the long and short of it is that there's a balance to be struck. Celtic will need to make that call very carefully as they consider offers for O'Riley.

They've already knocked back a couple from Serie A side Atalanta, while there remains very strong interest from the Premier League. Southampton appears to be the most likely potential suitor there. 

It would be remiss to mention that O'Riley has three years remaining on his contract, so, Celtic aren't in a position where buying clubs have them over a barrel. They're the ones holding all the aces. 

They can demand as big a fee as they feel they can realistically get, and they can get as many add-ons as possible as part of whatever agreements may be made when selling. 

The important thing to remember is that O'Riley has just scoped all of the club's Player of the Year awards. It's not out of the realms of possibility that his form dips, and then so does his value. There's a lot to consider for Rodgers and the Celtic board on that one. 

On Kyogo, he's proven time and again that he's the talisman and will rise to the big occasion. That's when he's at his best. Aged 29, the club isn't likely to make any real money off of him, so while he's still at his peak, does it make sense to sell? Not really.

Hatate had a horrible campaign last year, which was ravaged by multiple injuries. It would be in everyone's best interests that he sticks about, gets back to his best and then Celtic can see what kind of profit margins could be made there.