With less than three months until clubs across Europe kick off for next season, transfer rumours have been flying as teams prepare to battle once again across the continent. 

Much of the work over the summer is done behind doors, with many players taking some time away from the pitch to recover after last season. 

But staff behind the scenes will be working tirelessly to confirm transfer after transfer, and this summer could be one of the busiest windows in history. 

Cristiano Ronaldo shocked the footballing world by suggesting he wants to leave Real Madrid and Spain after tax fraud allegations and there will be plenty more drama ahead of the new season.

The biggest teams in Europe will be looking to boost their lineups, so expect the likes of Chelsea, Manchester United and Bayern Munich to all dig deep into the transfer fund, as they have done so often. 

Another team that hasn't been afraid to flex its financial muscle is Paris Saint-Germain. The club has made some huge signings over the past few years, including the likes of Angel Di Maria and Julian Draxler.

And there's now talk of them breaking the bank once again this summer.

According to Goal, the French club are ready to trigger a €100 million (£87.4 million) release clause for Atletico Madrid's goalkeeper Jan Oblak.   

Should they decide to, and the player expresses an interest to leave, Madrid will have little choice but to sell him.

However, even if Oblak becomes the second most expensive player in history should the clause be triggered, it would not be ideal for the Spanish club.     

They are currently serving a transfer ban and would be unable to reinvest any of that money until January, meaning they would not be able to buy a suitable replacement until midway through the season.

PSG aren't the only club interested in the Slovenia international, with Mourinho's United also tracking Oblak, in case they receive a bid for goalkeeper David de Gea.     

If the interest is as intense as rumoured, Atletico may have little option but to cash in on their first choice keeper and hope that backup Miguel Moya can step up until January.