Adding to the previous post I made some time ago, it would't surprise me if Celtic were quite open to this offer, as probably deep down sections of our own club were re Rooney.
Celtic seem a well run club with a clear business model. They regularly move lads on for decent money to the PL and have the space, facilities and manager to improve cheaper younger players with the profits generated. 25 million is a substantial fee for a Scottish team and I think they will be very tempted by an offer.
Unfortunately there will be limits to how far a lad can develop in a league that probably lacks meaningful competition. There comes an optimum moment to sell and I think that is probably approaching for Celtic. If he starts to get to 23/24 then his price begins to decrease as buying teams will see the ceiling he can reach will be lower as his years of improvement reduce. It's a bit like ourselves with Ross Barkley, in the end we probably waited too long to move him on to maximise the value in selling him, and with each year which went by his ceiling reduced.
Currently Tierney could go on to be a world class fullback but it's a good time to move.
For Celtic they could undoubtedly keep Tierney. He seems a refreshing loyal lad which is to be admired. However upwards of 25 million pounds may simply be more valuable to Celtic than Kieran Tierney.
None of this is intended to insult Celtic or the Scottish league. As I have reiterated Celtic are a massive club and like Rangers are much bigger than Everton. Brendan Rodgers was right when he said Celtic were bigger than Liverpool. It's a huge club. Neither have the finance of the English sides, but they have a huge area which is solidly working class and football mad. I hope they can bring through more Tierney's in time for their own teams. They could both field 6 or 8 lads or similar ability if they built up their academy roots.
Anyway my gut feeling is this could be one that moves forward.